ISO/IEC 23270:2006

INTERNATIONAL ISO/IEC
STANDARD 23270
Second edition
2006-09-01
Information technology — Programming
languages — C#
Technologies de l'information — Langages de programmation — C#

Reference number
©
ISO/IEC 2006
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ii © ISO/IEC 2006 – All rights reserved

Table of Contents
Foreword. xv
Introduction. xvi
1. Scope . 1
2. Conformance . 3
3. Normative references . 5
4. Terms and definitions . 7
5. Notational conventions. 9
6. Acronyms and abbreviations . 11
7. General description. 13
8. Language overview. 15
8.1 Getting started . 15
8.2 Types. 16
8.2.1 Predefined types. 17
8.2.2 Conversions. 19
8.2.3 Array types. 20
8.2.4 Type system unification . 22
8.3 Variables and parameters . 22
8.4 Automatic memory management . 25
8.5 Expressions . 27
8.6 Statements . 28
8.7 Classes. 31
8.7.1 Constants. 33
8.7.2 Fields. 33
8.7.3 Methods. 34
8.7.4 Properties . 35
8.7.5 Events. 36
8.7.6 Operators. 37
8.7.7 Indexers. 38
8.7.8 Instance constructors. 39
8.7.9 Finalizers. 40
8.7.10 Static constructors . 40
8.7.11 Inheritance. 41
8.7.12 Static classes . 42
8.7.13 Partial type declarations . 42
8.8 Structs. 43
8.9 Interfaces . 44
8.10 Delegates . 45
8.11 Enums. 46
8.12 Namespaces and assemblies. 46
8.13 Versioning . 48
8.14 Extern aliases. 49
8.15 Attributes. 51
8.16 Generics. 52
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8.16.1 Why generics?. 52
8.16.2 Creating and consuming generics . 53
8.16.3 Multiple type parameters. 54
8.16.4 Constraints . 54
8.16.5 Generic methods . 56
8.17 Anonymous methods. 56
8.18 Iterators . 59
8.19 Nullable types. 62
9. Lexical structure. 65
9.1 Programs . 65
9.2 Grammars. 65
9.2.1 Lexical grammar . 65
9.2.2 Syntactic grammar . 65
9.2.3 Grammar ambiguities. 66
9.3 Lexical analysis. 66
9.3.1 Line terminators . 67
9.3.2 Comments . 67
9.3.3 White space. 69
9.4 Tokens. 69
9.4.1 Unicode escape sequences . 69
9.4.2 Identifiers . 70
9.4.3 Keywords . 71
9.4.4 Literals . 72
9.4.4.1 Boolean literals. 72
9.4.4.2 Integer literals. 72
9.4.4.3 Real literals. 73
9.4.4.4 Character literals . 74
9.4.4.5 String literals . 75
9.4.4.6 The null literal . 76
9.4.5 Operators and punctuators. 77
9.5 Pre-processing directives. 77
9.5.1 Conditional compilation symbols . 78
9.5.2 Pre-processing expressions . 78
9.5.3 Declaration directives. 79
9.5.4 Conditional compilation directives . 80
9.5.5 Diagnostic directives. 82
9.5.6 Region control. 83
9.5.7 Line directives. 83
9.5.8 Pragma directives. 84
10. Basic concepts. 85
10.1 Application startup . 85
10.2 Application termination. 86
10.3 Declarations. 86
10.4 Members. 89
10.4.1 Namespace members. 89
10.4.2 Struct members . 89
10.4.3 Enumeration members . 89
10.4.4 Class members . 89
10.4.5 Interface members. 90
10.4.6 Array members. 90
10.4.7 Delegate members. 90
10.5 Member access . 90
10.5.1 Declared accessibility. 90
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10.5.2 Accessibility domains . 91
10.5.3 Protected access for instance members . 93
10.5.4 Accessibility constraints. 94
10.6 Signatures and overloading . 95
10.7 Scopes . 96
10.7.1 Name hiding. 98
10.7.1.1 Hiding through nesting. 98
10.7.1.2 Hiding through inheritance. 99
10.8 Namespace and type names. 100
10.8.1 Unqualified name. 102
10.8.2 Fully qualified names. 102
10.9 Automatic memory management . 103
10.10 Execution order . 105
11. Types . 107
11.1 Value types. 107
11.1.1 The System.ValueType type . 108
11.1.2 Default constructors . 108
11.1.3 Struct types. 109
11.1.4 Simple types. 109
11.1.5 Integral types. 110
11.1.6 Floating point types. 111
11.1.7 The decimal type. 111
11.1.8 The bool type . 112
11.1.9 Enumeration types. 112
11.2 Reference types . 112
11.2.1 Class types. 113
11.2.2 The object type. 113
11.2.3 The string type . 113
11.2.4 Interface types. 113
11.2.5 Array types. 114
11.2.6 Delegate types . 114
11.2.7 The null type . 114
11.3 Boxing and unboxing . 114
11.3.1 Boxing conversions. 114
11.3.2 Unboxing conversions. 115
11.4 Nullable types. 116
11.4.1 Members. 116
11.4.2 Implemented interfaces . 117
12. Variables . 119
12.1 Variable categories. 119
12.1.1 Static variables . 119
12.1.2 Instance variables. 119
12.1.2.1 Instance variables in classes. 119
12.1.2.2 Instance variables in structs. 120
12.1.3 Array elements . 120
12.1.4 Value parameters. 120
12.1.5 Reference parameters. 120
12.1.6 Output parameters . 120
12.1.7 Local variables . 121
12.2 Default values. 121
12.3 Definite assignment. 122
12.3.1 Initially assigned variables. 123
12.3.2 Initially unassigned variables. 123
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12.3.3 Precise rules for determining definite assignment . 123
12.3.3.1 General rules for statements. 124
12.3.3.2 Block statements, checked, and unchecked statements. 124
12.3.3.3 Expression statements . 124
12.3.3.4 Declaration statements . 124
12.3.3.5 If statements . 124
12.3.3.6 Switch statements. 125
12.3.3.7 While statements . 125
12.3.3.8 Do statements. 125
12.3.3.9 For statements . 125
12.3.3.10 Break, continue, and goto statements. 126
12.3.3.11 Throw statements . 126
12.3.3.12 Return statements . 126
12.3.3.13 Try-catch statements . 126
12.3.3.14 Try-finally statements . 127
12.3.3.15 Try-catch-finally statements. 127
12.3.3.16 Foreach statements . 128
12.3.3.17 Using statements . 128
12.3.3.18 Lock statements. 128
12.3.3.19 General rules for simple expressions . 128
12.3.3.20 General rules for expressions with embedded expressions . 129
12.3.3.21 Invocation expressions and object creation expressions . 129
12.3.3.22 Simple assignment expressions. 129
12.3.3.23 && expressions. 130
12.3.3.24 || expressions. 131
12.3.3.25 ! expressions. 131
12.3.3.26 ?: expressions . 132
12.3.3.27 Anonymous method expressions. 132
12.3.3.28 Yield statements . 133
12.3.3.29 ?? expressions. 133
12.4 Variable references. 133
12.5 Atomicity of variable references . 133
13. Conversions. 135
13.1 Implicit conversions . 135
13.1.1 Identity conversion. 135
13.1.2 Implicit numeric conversions. 135
13.1.3 Implicit enumeration conversions. 136
13.1.4 Implicit reference conversions . 136
13.1.5 Boxing conversions. 137
13.1.6 Implicit type parameter conversions . 137
13.1.7 Implicit constant expression conversions. 138
13.1.8 User-defined implicit conversions . 138
13.2 Explicit conversions . 138
13.2.1 Explicit numeric conversions. 138
13.2.2 Explicit enumeration conversions. 140
13.2.3 Explicit reference conversions . 140
13.2.4 Unboxing conversions. 141
13.2.5 Explicit type parameter conversions . 141
13.2.6 User-defined explicit conversions. 142
13.3 Standard conversions. 142
13.3.1 Standard implicit conversions. 142
13.3.2 Standard explicit conversions . 142
13.4 User-defined conversions. 142
13.4.1 Permitted user-defined conversions . 142
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13.4.2 Evaluation of user-defined conversions . 143
13.4.3 User-defined implicit conversions . 144
13.4.4 User-defined explicit conversions. 144
13.5 Anonymous method conversions . 145
13.6 Method group conversions . 146
13.7 Conversions involving nullable types . 147
13.7.1 Null type conversions. 148
13.7.2 Nullable conversions. 148
13.7.3 Lifted conversions. 148
14. Expressions . 149
14.1 Expression classifications . 149
14.1.1 Values of expressions. 150
14.2 Operators . 150
14.2.1 Operator precedence and associativity. 150
14.2.2 Operator overloading . 151
14.2.3 Unary operator overload resolution . 152
14.2.4 Binary operator overload resolution. 153
14.2.5 Candidate user-defined operators. 153
14.2.6 Numeric promotions. 153
14.2.6.1 Unary numeric promotions. 154
14.2.6.2 Binary numeric promotions. 154
14.2.7 Lifted operators . 155
14.3 Member lookup . 156
14.3.1 Base types . 157
14.4 Function members. 157
14.4.1 Argument lists . 159
14.4.2 Overload resolution. 161
14.4.2.1 Applicable function member. 162
14.4.2.2 Better function member. 163
14.4.2.3 Better conversion . 163
14.4.3 Function member invocation. 164
14.4.3.1 Invocations on boxed instances. 165
14.5 Primary expressions . 165
14.5.1 Literals . 166
14.5.2 Simple names . 166
14.5.2.1 Invariant meaning in blocks . 168
14.5.3 Parenthesized expressions. 168
14.5.4 Member access. 169
14.5.4.1 Identical simple names and type names . 170
14.5.5 Invocation expressions. 171
14.5.5.1 Method invocations. 171
14.5.5.2 Delegate invocations . 172
14.5.6 Element access . 173
14.5.6.1 Array access . 173
14.5.6.2 Indexer access . 173
14.5.7 This access . 174
14.5.8 Base access. 175
14.5.9 Postfix increment and decrement operators . 175
14.5.10 The new operator. 176
14.5.10.1 Object creation expressions. 176
14.5.10.2 Array creation expressions. 178
14.5.10.3 Delegate creation expressions . 179
14.5.11 The typeof operator. 182
14.5.12 The sizeof operator. 184
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14.5.13 The checked and unchecked operators. 184
14.5.14 Default value expression. 187
14.5.15 Anonymous methods. 187
14.5.15.1 Anonymous method signatures . 187
14.5.15.2 Anonymous method blocks. 188
14.5.15.3 Outer variables . 188
14.5.15.4 Anonymous method evaluation. 191
14.5.15.5 Implementation example. 191
14.6 Unary expressions . 194
14.6.1 Unary plus operator. 194
14.6.2 Unary minus operator. 194
14.6.3 Logical negation operator . 195
14.6.4 Bitwise complement operator . 195
14.6.5 Prefix increment and decrement operators. 195
14.6.6 Cast expressions. 196
14.7 Arithmetic operators. 197
14.7.1 Multiplication operator. 197
14.7.2 Division operator. 198
14.7.3 Remainder operator. 199
14.7.4 Addition operator . 200
14.7.5 Subtraction operator. 202
14.8 Shift operators . 204
14.9 Relational and type-testing operators. 205
14.9.1 Integer comparison operators. 206
14.9.2 Floating-point comparison operators . 207
14.9.3 Decimal comparison operators. 207
14.9.4 Boolean equality operators. 208
14.9.5 Enumeration comparison operators. 208
14.9.6 Reference type equality operators.
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