C# Language Specification

C#

Language Specification

Working Draft WD3.15

January 25 2017

Table of Contents

Foreword1

Introduction2

1. Scope3

2. Conformance5

3. Normative references7

4. Terms and definitions9

5. Acronyms and abbreviations13

6. General description15

7. Language overview17

8. Lexical structure18

8.1 Programs18

8.2 Grammars18

8.2.1 General18

8.2.2 Grammar notation18

8.2.3 Lexical grammar19

8.2.4 Syntactic grammar20

8.2.5 Grammar ambiguities20

8.3 Lexical analysis21

8.3.1 General21

8.3.2 Line terminators21

8.3.3 Comments22

8.3.4 White space23

8.4 Tokens23

8.4.1 General23

8.4.2 Unicode character escape sequences24

8.4.3 Identifiers24

8.4.4 Keywords26

8.4.5 Literals27

8.4.5.1 General27

8.4.5.2 Boolean literals27

8.4.5.3 Integer literals27

8.4.5.4 Real literals28

8.4.5.5 Character literals29

8.4.5.6 String literals30

8.4.5.7 The null literal32

8.4.6 Operators and punctuators32

8.5 Pre-processing directives33

8.5.1 General33

8.5.2 Conditional compilation symbols34

8.5.3 Pre-processing expressions34

8.5.4 Definition directives35

8.5.5 Conditional compilation directives36

8.5.6 Diagnostic directives38

8.5.7 Region directives39

8.5.8 Line directives39

8.5.9 Pragma directives40

8.5.9.1 General40

8.5.9.2 Pragma warning40

9. Basic concepts43

9.1 Application startup43

9.2 Application termination44

9.3 Declarations44

9.4 Members47

9.4.1 General47

9.4.2 Namespace members47

9.4.3 Struct members47

9.4.4 Enumeration members47

9.4.5 Class members48

9.4.6 Interface members48

9.4.7 Array members48

9.4.8 Delegate members48

9.5 Member access48

9.5.1 General48

9.5.2 Declared accessibility48

9.5.3 Accessibility domains49

9.5.4 Protected access51

9.5.5 Accessibility constraints53

9.6 Signatures and overloading53

9.7 Scopes55

9.7.1 General55

9.7.2 Name hiding57

9.7.2.1 General57

9.7.2.2 Hiding through nesting58

9.7.2.3 Hiding through inheritance58

9.8 Namespace and type names59

9.8.1 General59

9.8.2 Fully qualified names61

9.9 Automatic memory management62

9.10 Execution order64

10. Types67

10.1 General67

10.2 Reference types67

10.2.1 General67

10.2.2 Class types68

10.2.3 The object type68

10.2.4 The dynamic type69

10.2.5 The string type69

10.2.6 Interface types69

10.2.7 Array types69

10.2.8 Delegate types69

10.3 Value types69

10.3.1 General69

10.3.2 The System.ValueType type70

10.3.3 Default constructors70

10.3.4 Struct types71

10.3.5 Simple types71

10.3.6 Integral types72

10.3.7 Floating-point types73

10.3.8 The decimal type74

10.3.9 The bool type75

10.3.10 Enumeration types75

10.3.11 Nullable value types75

10.3.12 Boxing and unboxing76

10.4 Constructed types76

10.4.1 General76

10.4.2 Type arguments77

10.4.3 Open and closed types77

10.4.4 Bound and unbound types77

10.4.5 Satisfying constraints77

10.5 Type parameters78

10.6 Expression tree types79

10.7 The dynamic type80

11. Variables81

11.1 General81

11.2 Variable categories81

11.2.1 General81

11.2.2 Static variables81

11.2.3 Instance variables81

11.2.3.1 General81

11.2.3.2 Instance variables in classes82

11.2.3.3 Instance variables in structs82

11.2.4 Array elements82

11.2.5 Value parameters82

11.2.6 Reference parameters82

11.2.7 Output parameters83

11.2.8 Local variables83

11.3 Default values84

11.4 Definite assignment84

11.4.1 General84

11.4.2 Initially assigned variables85

11.4.3 Initially unassigned variables85

11.4.4 Precise rules for determining definite assignment85

11.4.4.1 General85

11.4.4.2 General rules for statements86

11.4.4.3 Block statements, checked, and unchecked statements86

11.4.4.4 Expression statements86

11.4.4.5 Declaration statements87

11.4.4.6 If statements87

11.4.4.7 Switch statements87

11.4.4.8 While statements87

11.4.4.9 Do statements87

11.4.4.10 For statements88

11.4.4.11 Break, continue, and goto statements88

11.4.4.12 Throw statements88

11.4.4.13 Return statements88

11.4.4.14 Try-catch statements89

11.4.4.15 Try-finally statements89

11.4.4.16 Try-catch-finally statements89

11.4.4.17 Foreach statements90

11.4.4.18 Using statements90

11.4.4.19 Lock statements90

11.4.4.20 Yield statements91

11.4.4.21 General rules for constant expressions91

11.4.4.22 General rules for simple expressions91

11.4.4.23 General rules for expressions with embedded expressions91

11.4.4.24 Invocation expressions and object creation expressions92

11.4.4.25 Simple assignment expressions92

11.4.4.26 && expressions93

11.4.4.27 || expressions94

11.4.4.28 ! expressions94

11.4.4.29 ?? expressions95

11.4.4.30 ?: expressions95

11.4.4.31 Anonymous functions95

11.5 Variable references96

11.6 Atomicity of variable references96

12. Conversions97

12.1 General97

12.2 Implicit conversions97

12.2.1 General97

12.2.2 Identity conversion98

12.2.3 Implicit numeric conversions98

12.2.4 Implicit enumeration conversions98

12.2.5 Implicit nullable conversions98

12.2.6 Null literal conversions98

12.2.7 Implicit reference conversions99

12.2.8 Boxing conversions99

12.2.9 Implicit dynamic conversions101

12.2.10 Implicit constant expression conversions101

12.2.11 Implicit conversions involving type parameters101

12.2.12 User-defined implicit conversions102

12.2.13 Anonymous function conversions and method group conversions102

12.3 Explicit conversions102

12.3.1 General102

12.3.2 Explicit numeric conversions103

12.3.3 Explicit enumeration conversions104

12.3.4 Explicit nullable conversions105

12.3.5 Explicit reference conversions105

12.3.6 Unboxing conversions106

12.3.7 Explicit dynamic conversions106

12.3.8 Explicit conversions involving type parameters107

12.3.9 User-defined explicit conversions108

12.4 Standard conversions108

12.4.1 General108

12.4.2 Standard implicit conversions108

12.4.3 Standard explicit conversions109

12.5 User-defined conversions109

12.5.1 General109

12.5.2 Permitted user-defined conversions109

12.5.3 Lifted conversion operators109

12.5.4 Evaluation of user-defined conversions109

12.5.5 User-defined implicit conversions110

12.5.6 User-defined explicit conversions111

12.6 Conversions involving nullable types112

12.6.1 Nullable Conversions112

12.6.2 Lifted conversions113

12.7 Anonymous function conversions113

12.7.1 General113

12.7.2 Evaluation of anonymous function conversions to delegate types114

12.7.3 Evaluation of anonymous function conversions to expression tree types115

12.7.4 Implementation example115

12.8 Method group conversions118

13. Expressions120

13.1 General120

13.2 Expression classifications120

13.2.1 General120

13.2.2 Values of expressions121

13.3 Static and Dynamic Binding121

13.3.1 General121

13.3.2 Binding-time122

13.3.3 Dynamic binding122

13.3.4 Types of subexpressions123

13.4 Operators123

13.4.1 General123

13.4.2 Operator precedence and associativity123

13.4.3 Operator overloading124

13.4.4 Unary operator overload resolution126

13.4.5 Binary operator overload resolution126

13.4.6 Candidate user-defined operators126

13.4.7 Numeric promotions127

13.4.7.1 General127

13.4.7.2 Unary numeric promotions127

13.4.7.3 Binary numeric promotions127

13.4.8 Lifted operators128

13.5 Member lookup129

13.5.1 General129

13.5.2 Base types130

13.6 Function members130

13.6.1 General130

13.6.2 Argument lists133

13.6.2.1 General133

13.6.2.2 Corresponding parameters134

13.6.2.3 Run-time evaluation of argument lists135

13.6.3 Type inference136

13.6.3.1 General136

13.6.3.2 The first phase137

13.6.3.3 The second phase137

13.6.3.4 Input types138

13.6.3.5 Output types138

13.6.3.6 Dependence138

13.6.3.7 Output type inferences138

13.6.3.8 Explicit parameter type inferences138

13.6.3.9 Exact inferences138

13.6.3.10 Lower-bound inferences139

13.6.3.11 Upper-bound inferences139

13.6.3.12 Fixing140

13.6.3.13 Inferred return type140

13.6.3.14 Type inference for conversion of method groups141

13.6.3.15 Finding the best common type of a set of expressions142

13.6.4 Overload resolution142

13.6.4.1 General142

13.6.4.2 Applicable function member143

13.6.4.3 Better function member143