C# Language Reference

Table of Contents
1. Introduction.......................................................................................................................................... 1
1.1 Hello, world .......................................................................................................................................1
1.2 Automatic memory management ..........................................................................................................2
1.3 Types.................................................................................................................................................4
1.4 Predefined types .................................................................................................................................5
1.5 Array types ........................................................................................................................................7
1.6 Type system unification .......................................................................................................................9
1.7 Statements .......................................................................................................................................10
1.7.1 Statement lists and blocks ............................................................................................................10
1.7.2 Labeled statements and goto statements ......................................................................................10
1.7.3 Local declarations of constants and variables.................................................................................11
1.7.4 Expression statements..................................................................................................................11
1.7.5 The if statement ..........................................................................................................................11
1.7.6 The switch statement ...................................................................................................................12
1.7.7 The while statement ....................................................................................................................12
1.7.8 The do statement........................................................................................................................13
1.7.9 The for statement ........................................................................................................................13
1.7.10 The foreach statement.............................................................................................................13
1.7.11 The break statement and the continue statement .....................................................................14
1.7.12 The return statement...............................................................................................................14
1.7.13 The throw statement.................................................................................................................14
1.7.14 The try statement.....................................................................................................................14
1.7.15 The checked and unchecked statements ..................................................................................14
1.7.16 The lock statement...................................................................................................................14
1.8 Classes ............................................................................................................................................14
1.9 Structs .............................................................................................................................................15
1.10 Interfaces .......................................................................................................................................15
1.11 Delegates .......................................................................................................................................17
1.12 Enums............................................................................................................................................18
1.13 Namespaces ...................................................................................................................................18
1.14 Properties.......................................................................................................................................19
1.15 Indexers .........................................................................................................................................20
1.16 Events............................................................................................................................................21
1.17 Versioning......................................................................................................................................22
1.18 Attributes .......................................................................................................................................24
2. Lexical structure ................................................................................................................................. 27
2.1 Phases of translation..........................................................................................................................27
2.2 Grammar notation.............................................................................................................................27
2.3 Pre-processing ..................................................................................................................................28
2.3.1 Pre-processing declarations ..........................................................................................................28
2.3.2 #if, #elif, #else, #endif .................................................................................................................29
2.3.3 Pre-processing control lines .........................................................................................................30
2.3.4 #line ..........................................................................................................................................31
2.3.5 Pre-processing identifiers.............................................................................................................31
2.3.6 Pre-processing expressions...........................................................................................................31
2.3.7 Interaction with white space.........................................................................................................32
2.4 Lexical analysis ................................................................................................................................33
2.4.1 Input..........................................................................................................................................33
2.4.2 Input characters..........................................................................................................................33
2.4.3 Line terminators ..........................................................................................................................33
2.4.4 Comments..................................................................................................................................33
2.4.5 White space ...............................................................................................................................33
2.4.6 Tokens.......................................................................................................................................33
2.5 Processing of Unicode character escape sequences ..............................................................................34
2.5.1 Identifiers ..................................................................................................................................34
2.5.2 Keywords ..................................................................................................................................36
2.5.3 Literals ......................................................................................................................................36
2.5.3.1 Boolean literals .....................................................................................................................36
2.5.3.2 Integer literals .......................................................................................................................36
2.5.3.3 Real literals ...........................................................................................................................37
2.5.3.4 Character literals ...................................................................................................................38
2.5.3.5 String literals........................................................................................................................39
2.5.3.6 The null literal.......................................................................................................................40
2.5.4 Operators and punctuators............................................................................................................40
3. Basic concepts ..................................................................................................................................... 41
3.1 Declarations .....................................................................................................................................41
3.2 Members..........................................................................................................................................43
3.2.1 Namespace members...................................................................................................................43
3.2.2 Struct members ...........................................................................................................................43
3.2.3 Enumeration members .................................................................................................................44
3.2.4 Class members...........................................................................................................................44
3.2.5 Interface members.......................................................................................................................44
3.2.6 Array members ...........................................................................................................................44
3.2.7 Delegate members.......................................................................................................................44
3.3 Member access.................................................................................................................................44
3.3.1 Declared accessibility ..................................................................................................................44
3.3.2 Accessibility domains ..................................................................................................................45
3.3.3 Protected access.........................................................................................................................47
3.3.4 Accessibility constraints...............................................................................................................48
3.4 Signatures and overloading.................................................................................................................49
3.5 Scopes .............................................................................................................................................50
3.5.1 Name hiding...............................................................................................................................52
3.5.1.1 Hiding through nesting...........................................................................................................52
3.5.1.2 Hiding through inheritance.....................................................................................................53
3.6 Namespace and type names................................................................................................................54
3.6.1 Fully qualified names ..................................................................................................................55
4. Types .................................................................................................................................................. 57
4.1 Value types ......................................................................................................................................57
4.1.1 Default constructors ....................................................................................................................58
4.1.2 Struct types................................................................................................................................59
4.1.3 Simple types ...............................................................................................................................59
4.1.4 Integral types ..............................................................................................................................60
4.1.5 Floating point types .....................................................................................................................61
4.1.6 The decimal type .........................................................................................................................62
4.1.7 The bool type ............................................................................................................................63
4.1.8 Enumeration types.......................................................................................................................63
4.2 Reference types................................................................................................................................63
4.2.1 Class types.................................................................................................................................64
4.2.2 The object type...........................................................................................................................64
4.2.3 The string type ............................................................................................................................64
4.2.4 Interface types ............................................................................................................................64
4.2.5 Array types................................................................................................................................64
4.2.6 Delegate types ............................................................................................................................64
4.3 Boxing and unboxing .........................................................................................................................65
4.3.1 Boxing conversions .....................................................................................................................65
4.3.2 Unboxing conversions .................................................................................................................66
5. Variables ............................................................................................................................................ 67
5.1 Variable categories ............................................................................................................................67
5.1.1 Static variables...........................................................................................................................67
5.1.2 Instance variables ........................................................................................................................67
5.1.2.1 Instance variables in classes...................................................................................................67
5.1.2.2 Instance variables in structs....................................................................................................68
5.1.3 Array elements...........................................................................................................................68
5.1.4 Value parameters ........................................................................................................................68
5.1.5 Reference parameters ..................................................................................................................68
5.1.6 Output parameters......................................................................................................................68
5.1.7 Local variables...........................................................................................................................69
5.2 Default values ..................................................................................................................................69
5.3 Definite assignment ...........................................................................................................................69
5.3.1 Initially assigned variables ...........................................................................................................72
5.3.2 Initially unassigned variables .......................................................................................................72
5.4 Variable references ............................................................................................................................72
6. Conversions ........................................................................................................................................ 73
6.1 Implicit conversions..........................................................................................................................73
6.1.1 Identity conversion.....................................................................................................................73
6.1.2 Implicit numeric conversions........................................................................................................73
6.1.3 Implicit enumeration conversions .................................................................................................74
6.1.4 Implicit reference conversions ......................................................................................................74
6.1.5 Boxing conversions .....................................................................................................................74
6.1.6 Implicit constant expression conversions.......................................................................................74
6.1.7 User-defined implicit conversions.................................................................................................75
6.2 Explicit conversions..........................................................................................................................75
6.2.1 Explicit numeric conversions........................................................................................................75
6.2.2 Explicit enumeration conversions .................................................................................................76
6.2.3 Explicit reference conversions ......................................................................................................76
6.2.4 Unboxing conversions .................................................................................................................77
6.2.5 User-defined explicit conversions .................................................................................................77
6.3 Standard conversions .........................................................................................................................77
6.3.1 Standard implicit conversions.......................................................................................................77
6.3.2 Standard explicit conversions .......................................................................................................78
6.4 User-defined conversions ...................................................................................................................78
6.4.1 Permitted user-defined conversions...............................................................................................78
6.4.2 Evaluation of user-defined conversions .........................................................................................78
6.4.3 User-defined implicit conversions.................................................................................................79
6.4.4 User-defined explicit conversions .................................................................................................80
7. Expressions ......................................................................................................................................... 81
7.1 Expression classifications ...................................................................................................................81
7.1.1 Values of expressions ..................................................................................................................82
7.2 Operators.........................................................................................................................................82
7.2.1 Operator precedence and associativity...........................................................................................82
7.2.2 Operator overloading ...................................................................................................................83
7.2.3 Unary operator overload resolution...............................................................................................84
7.2.4 Binary operator overload resolution ..............................................................................................85
7.2.5 Candidate user-defined operators..................................................................................................85
7.2.6 Numeric promotions ....................................................................................................................85
7.2.6.1 Unary numeric promotions .....................................................................................................86
7.2.6.2 Binary numeric promotions ....................................................................................................86
7.3 Member lookup ................................................................................................................................86
7.3.1 Base types .................................................................................................................................87
7.4 Function members .............................................................................................................................87
7.4.1 Argument lists............................................................................................................................89
7.4.2 Overload resolution .....................................................................................................................91
7.4.2.1 Applicable function member ..................................................................................................91
7.4.2.2 Better function member .........................................................................................................92
7.4.2.3 Better conversion...................................................................................................................92
7.4.3 Function member invocation........................................................................................................92
7.4.3.1 Invocations on boxed instances ..............................................................................................93
7.4.4 Virtual function member lookup ...................................................................................................94
7.4.5 Interface function member lookup ................................................................................................94
7.5 Primary expressions ...........................................................................................................................94
7.5.1 Literals ......................................................................................................................................94
7.5.2 Simple names.............................................................................................................................94
7.5.2.1 Invariant meaning in blocks ...................................................................................................95
7.5.3 Parenthesized expressions ............................................................................................................96
7.5.4 Member access ...........................................................................................................................96
7.5.4.1 Identical simple names and type names...................................................................................98
7.5.5 Invocation expressions .................................................................................................................98
7.5.5.1 Method invocations ...............................................................................................................99
7.5.5.2 Delegate invocations..............................................................................................................99
7.5.6 Element access......................................................................................................................... 100
7.5.6.1 Array access ....................................................................................................................... 100
7.5.6.2 Indexer access..................................................................................................................... 100
7.5.6.3 String indexing.................................................................................................................... 101
7.5.7 This access ............................................................................................................................... 101
7.5.8 Base access.............................................................................................................................. 102
7.5.9 Postfix increment and decrement operators ................................................................................. 102
7.5.10 new operator ........................................................................................................................... 103
7.5.10.1 Object creation expressions ................................................................................................ 103
7.5.10.2 Array creation expressions ................................................................................................. 104
7.5.10.3 Delegate creation expressions ............................................................................................. 106
7.5.11 typeof operator ................................................................................................................. 107
7.5.12 sizeof operator ................................................................................................................. 108
7.5.13 checked and unchecked operators..................................................................................... 108
7.6 Unary expressions........................................................................................................................... 110
7.6.1 Unary plus operator ................................................................................................................... 110
7.6.2 Unary minus operator ................................................................................................................ 111
7.6.3 Logical negation operator........................................................................................................... 111
7.6.4 Bitwise complement operator ..................................................................................................... 111
7.6.5 Indirection operator ................................................................................................................... 112
7.6.6 Address operator ....................................................................................................................... 112
7.6.7 Prefix increment and decrement operators................................................................................... 112
7.6.8 Cast expressions ........................................................................................................................ 113
7.7 Arithmetic operators ........................................................................................................................ 113
7.7.1 Multiplication operator .............................................................................................................. 113
7.7.2 Division operator....................................................................................................................... 114
7.7.3 Remainder operator ................................................................................................................... 115
7.7.4 Addition operator ...................................................................................................................... 116
7.7.5 Subtraction operator .................................................................................................................. 117
7.8 Shift operators................................................................................................................................ 118
7.9 Relational operators........................................................................................................................ 119
7.9.1 Integer comparison operators ..................................................................................................... 120
7.9.2 Floating-point comparison operators........................................................................................... 121
7.9.3 Decimal comparison operators ................................................................................................... 121
7.9.4 Boolean equality operators......................................................................................................... 122
7.9.5 Enumeration comparison operators............................................................................................. 122
7.9.6 Reference type equality operators............................................................................................... 122
7.9.7 String equality operators ............................................................................................................ 123
7.9.8 Delegate equality operators ........................................................................................................ 124
7.9.9 The is operator .......................................................................................................................... 124
7.10 Logical operators.......................................................................................................................... 124
7.10.1 Integer logical operators........................................................................................................... 124
7.10.2 Enumeration logical operators .................................................................................................. 125
7.10.3 Boolean logical operators......................................................................................................... 125
7.11 Conditional logical operators.......................................................................................................... 125
7.11.1 Boolean conditional logical operators ....................................................................................... 126
7.11.2 User-defined conditional logical operators ................................................................................ 126
7.12 Conditional operator ...................................................................................................................... 127
7.13 Assignment operators..................................................................................................................... 127
7.13.1 Simple assignment................................................................................................................... 128
7.13.2 Compound assignment ............................................................................................................. 130
7.13.3 Event assignment..................................................................................................................... 130
7.14 Expression.................................................................................................................................... 130
7.15 Constant expressions ...................................................................................................................... 131
7.16 Boolean expressions...................................................................................................................... 132
8. Statements .........................................................................................................................................133
8.1 End points and reachability............................................................................................................... 133
8.2 Blocks............................................................................................................................................ 135
8.2.1 Statement lists.......................................................................................................................... 135
8.3 The empty statement....................................................................................................................... 135
8.4 Labeled statements .......................................................................................................................... 136
8.5 Declaration statements..................................................................................................................... 136
8.5.1 Local variable declarations ......................................................................................................... 136
8.5.2 Local constant declarations ........................................................................................................ 137
8.6 Expression statements..................................................................................................................... 138
8.7 Selection statements ........................................................................................................................ 138
8.7.1 The if statement ........................................................................................................................ 138
8.7.2 The switch statement ................................................................................................................. 139
8.8 Iteration statements......................................................................................................................... 142
8.8.1 The while statement .................................................................................................................. 143
8.8.2 The do statement...................................................................................................................... 143
8.8.3 The for statement ...................................................................................................................... 144
8.8.4 The foreach statement............................................................................................................. 145
8.9 Jump statements .............................................................................................................................. 146
8.9.1 The break statement .................................................................................................................. 146
8.9.2 The continue statement.............................................................................................................. 147
8.9.3 The goto statement................................................................................................................... 147
8.9.4 The return statement.................................................................................................................. 148
8.9.5 The throw statement .................................................................................................................. 149
8.10 The try statement.......................................................................................................................... 150
8.11 The checked and unchecked statements........................................................................................... 152
8.12 The lock statement........................................................................................................................ 152
9. Namespaces .......................................................................................................................................155
9.1 Compilation units ............................................................................................................................ 155
9.2 Namespace declarations ................................................................................................................... 155
9.3 Using directives.............................................................................................................................. 156
9.3.1 Using alias directives................................................................................................................. 157
9.3.2 Using namespace directives ....................................................................................................... 159
9.4 Namespace members ....................................................................................................................... 161
9.5 Type declarations............................................................................................................................ 161
10. Classes .............................................................................................................................................163
10.1 Class declarations .......................................................................................................................... 163
10.1.1 Class modifiers....................................................................................................................... 163
10.1.1.1 Abstract classes ................................................................................................................. 163
10.1.1.2 Sealed classes ................................................................................................................... 164
10.1.2 Class base specification............................................................................................................ 164
10.1.2.1 Base classes ...................................................................................................................... 164
10.1.2.2 Interface implementations .................................................................................................. 165
10.1.3 Class body.............................................................................................................................. 166
10.2 Class members .............................................................................................................................. 166
10.2.1 Inheritance .............................................................................................................................. 167
10.2.2 The new modifier .................................................................................................................... 167
10.2.3 Access modifiers ..................................................................................................................... 168
10.2.4 Constituent types ..................................................................................................................... 168
10.2.5 Static and instance members .................................................................................................... 168
10.2.6 Nested types ........................................................................................................................... 169
10.3 Constants ..................................................................................................................................... 169
10.4 Fields ........................................................................................................................................... 170
10.4.1 Static and instance fields .......................................................................................................... 171
10.4.2 Readonly fields........................................................................................................................ 172
10.4.2.1 Using static readonly fields for constants ............................................................................ 172
10.4.2.2 Versioning of constants and static readonly fields ................................................................ 172
10.4.3 Field initialization................................................................................................................... 173
10.4.4 Variable initializers.................................................................................................................. 173
10.4.4.1 Static field initialization ..................................................................................................... 174
10.4.4.2 Instance field initialization ................................................................................................. 174
10.5 Methods ....................................................................................................................................... 175
10.5.1 Method parameters.................................................................................................................. 176
10.5.1.1 Value parameters............................................................................................................... 177
10.5.1.2 Reference parameters ........................................................................................................ 177
10.5.1.3 Output parameters ............................................................................................................. 178
10.5.1.4 Params parameters ............................................................................................................ 178
10.5.2 Static and instance methods...................................................................................................... 180
10.5.3 Virtual methods ....................................................................................................................... 180
10.5.4 Override methods .................................................................................................................... 182
10.5.5 Abstract methods..................................................................................................................... 183
10.5.6 External methods ..................................................................................................................... 184
10.5.7 Method body ........................................................................................................................... 185
10.5.8 Method overloading................................................................................................................. 185
10.6 Properties..................................................................................................................................... 185
10.6.1 Static properties...................................................................................................................... 186
10.6.2 Accessors ............................................................................................................................... 187
10.6.3 Virtual, override, and abstract accessors.................................................................................... 191
10.7 Events.......................................................................................................................................... 193
10.8 Indexers ....................................................................................................................................... 196
10.8.1 Indexer overloading ................................................................................................................. 199
10.9 Operators ..................................................................................................................................... 199
10.9.1 Unary operators...................................................................................................................... 200
10.9.2 Binary operators...................................................................................................................... 200
10.9.3 Conversion operators ............................................................................................................... 200
10.10 Instance constructors................................................................................................................... 202
10.10.1 Constructor initializers ........................................................................................................... 202
10.10.2 Instance variable initializers ................................................................................................... 203
10.10.3 Constructor execution ............................................................................................................ 203
10.10.4 Default constructors............................................................................................................... 205
10.10.5 Private constructors ............................................................................................................... 205
10.10.6 Optional constructor parameters ............................................................................................. 206
10.11 Destructors................................................................................................................................. 206
10.12 Static constructors....................................................................................................................... 207
10.12.1 Class loading and initialization ............................................................................................... 208
11. Structs .............................................................................................................................................211
11.1 Struct declarations......................................................................................................................... 211
11.1.1 Struct modifiers...................................................................................................................... 211
11.1.2 Interfaces............................................................................................................................... 211
11.1.3 Struct body............................................................................................................................. 211
11.2 Struct members............................................................................................................................. 211
11.3 Struct examples ............................................................................................................................. 211
11.3.1 Database integer type............................................................................................................... 211
11.3.2 Database boolean type ............................................................................................................. 213
12. Arrays ..............................................................................................................................................215
12.1 Array types .................................................................................................................................. 215
12.1.1 The System.Array type......................................................................................................... 216
12.2 Array creation............................................................................................................................... 216
12.3 Array element access ..................................................................................................................... 216
12.4 Array members............................................................................................................................. 216
12.5 Array covariance ........................................................................................................................... 216
12.6 Array initializers........................................................................................................................... 217
13. Interfaces .........................................................................................................................................219
13.1 Interface declarations ..................................................................................................................... 219
13.1.1 Interface modifiers................................................................................................................... 219
13.1.2 Base interfaces....................................................................................................................... 219
13.1.3 Interface body ......................................................................................................................... 220
13.2 Interface members ......................................................................................................................... 220
13.2.1 Interface methods .................................................................................................................... 221
13.2.2 Interface properties.................................................................................................................. 221
13.2.3 Interface events....................................................................................................................... 222
13.2.4 Interface indexers .................................................................................................................... 222
13.2.5 Interface member access .......................................................................................................... 222
13.3 Fully qualified interface member names.......................................................................................... 224
13.4 Interface implementations............................................................................................................... 224
13.4.1 Explicit interface member implementations ............................................................................... 225
13.4.2 Interface mapping .................................................................................................................... 227
13.4.3 Interface implementation inheritance ........................................................................................ 229
13.4.4 Interface re-implementation...................................................................................................... 231
13.4.5 Abstract classes and interfaces ................................................................................................. 232
14. Enums ..............................................................................................................................................233
14.1 Enum declarations......................................................................................................................... 233
14.2 Enum members............................................................................................................................. 234
14.3 Enum values and operations............................................................................................................ 236
15. Delegates..........................................................................................................................................237
15.1 Delegate declarations ..................................................................................................................... 237
15.1.1 Delegate modifiers................................................................................................................... 237
16. Exceptions .......................................................................................................................................239
17. Attributes ........................................................................................................................................241
17.1 Attribute classes ............................................................................................................................ 241
17.1.1 The AttributeUsage attribute ............................................................................................... 241
17.1.2 Positional and named parameters.............................................................................................. 242
17.1.3 Attribute parameter types......................................................................................................... 242
17.2 Attribute specification .................................................................................................................... 243
17.3 Attribute instances ......................................................................................................................... 245
17.3.1 Compilation of an attribute ....................................................................................................... 245
17.3.2 Run-time retrieval of an attribute instance ................................................................................. 245
17.4 Reserved attributes........................................................................................................................ 245
17.4.1 The AttributeUsage attribute ............................................................................................... 246
17.4.2 The Conditional attribute ..................................................................................................... 246
17.4.3 The Obsolete attribute ........................................................................................................... 248
18. Versioning ........................................................................................................................................251
19. Unsafe code ......................................................................................................................................253
19.1 Unsafe code ................................................................................................................................. 253
19.2 Pointer types................................................................................................................................. 253
20. Interoperability................................................................................................................................255
20.1 Attributes ..................................................................................................................................... 255
20.1.1 The COMImpot attribute ......................................................................................................... 255
20.1.2 The COMSourceInterfaces attribute..................................................................................... 255
20.1.3 The COMVisibility attribute ................................................................................................. 255
20.1.4 The DispId attribute ............................................................................................................... 256
20.1.5 The DllImpor attribute ......................................................................................................... 256
20.1.6 The GlobalObject attribute ................................................................................................... 257
20.1.7 The Guid attribute ................................................................................................................... 257
20.1.8 The HasDefaultInterface attribute..................................................................................... 257
20.1.9 The ImporedFromCOM attribute ............................................................................................. 257
20.1.10 The In and Out attributes ...................................................................................................... 257
20.1.11 The InterfaceType attribute ............................................................................................... 258
20.1.12 The IsCOMRegisterFunction attribute ............................................................................... 258
20.1.13 The Marshal attribute ........................................................................................................... 258
20.1.14 The Name attribute ................................................................................................................. 259
20.1.15 The NoIDispatch attribute ................................................................................................... 259
20.1.16 The NonSerialized attribute ............................................................................................... 259
20.1.17 The Predeclared attribute ................................................................................................... 260
20.1.18 The ReturnsHResult attribute ............................................................................................. 260
20.1.19 The Serializable attribute ................................................................................................. 260
20.1.20 The StructLayout attribute ................................................................................................. 260
20.1.21 The StructOffset attribute ................................................................................................. 261
20.1.22 The TypeLibFunc attribute ................................................................................................... 261
20.1.23 The TypeLibType attribute ................................................................................................... 261
20.1.24 The TypeLibVar attribute ..................................................................................................... 262
20.2 Supporting enums .......................................................................................................................... 262
21. References .......................................................................................................................................265

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