- •Foreword
- •Introduction
- •Scope
- •Conformance
- •Normative references
- •Definitions
- •Notational conventions
- •Acronyms and abbreviations
- •General description
- •Language overview
- •Getting started
- •Types
- •Predefined types
- •Conversions
- •Array types
- •Type system unification
- •Variables and parameters
- •Automatic memory management
- •Expressions
- •Statements
- •Classes
- •Constants
- •Fields
- •Methods
- •Properties
- •Events
- •Operators
- •Indexers
- •Instance constructors
- •Destructors
- •Static constructors
- •Inheritance
- •Static classes
- •Partial type declarations
- •Structs
- •Interfaces
- •Delegates
- •Enums
- •Namespaces and assemblies
- •Versioning
- •Extern Aliases
- •Attributes
- •Generics
- •Why generics?
- •Creating and consuming generics
- •Multiple type parameters
- •Constraints
- •Generic methods
- •Anonymous methods
- •Iterators
- •Lexical structure
- •Programs
- •Grammars
- •Lexical grammar
- •Syntactic grammar
- •Grammar ambiguities
- •Lexical analysis
- •Line terminators
- •Comments
- •White space
- •Tokens
- •Unicode escape sequences
- •Identifiers
- •Keywords
- •Literals
- •Boolean literals
- •Integer literals
- •Real literals
- •Character literals
- •String literals
- •The null literal
- •Operators and punctuators
- •Pre-processing directives
- •Conditional compilation symbols
- •Pre-processing expressions
- •Declaration directives
- •Conditional compilation directives
- •Diagnostic directives
- •Region control
- •Line directives
- •Pragma directives
- •Basic concepts
- •Application startup
- •Application termination
- •Declarations
- •Members
- •Namespace members
- •Struct members
- •Enumeration members
- •Class members
- •Interface members
- •Array members
- •Delegate members
- •Member access
- •Declared accessibility
- •Accessibility domains
- •Protected access for instance members
- •Accessibility constraints
- •Signatures and overloading
- •Scopes
- •Name hiding
- •Hiding through nesting
- •Hiding through inheritance
- •Namespace and type names
- •Unqualified name
- •Fully qualified names
- •Automatic memory management
- •Execution order
- •Types
- •Value types
- •The System.ValueType type
- •Default constructors
- •Struct types
- •Simple types
- •Integral types
- •Floating point types
- •The decimal type
- •The bool type
- •Enumeration types
- •Reference types
- •Class types
- •The object type
- •The string type
- •Interface types
- •Array types
- •Delegate types
- •Boxing and unboxing
- •Boxing conversions
- •Unboxing conversions
- •Variables
- •Variable categories
- •Static variables
- •Instance variables
- •Instance variables in classes
- •Instance variables in structs
- •Array elements
- •Value parameters
- •Reference parameters
- •Output parameters
- •Local variables
- •Default values
- •Definite assignment
- •Initially assigned variables
- •Initially unassigned variables
- •Precise rules for determining definite assignment
- •General rules for statements
- •Block statements, checked, and unchecked statements
- •Expression statements
- •Declaration statements
- •If statements
- •Switch statements
- •While statements
- •Do statements
- •For statements
- •Break, continue, and goto statements
- •Throw statements
- •Return statements
- •Try-catch statements
- •Try-finally statements
- •Try-catch-finally statements
- •Foreach statements
- •Using statements
- •Lock statements
- •General rules for simple expressions
- •General rules for expressions with embedded expressions
- •Invocation expressions and object creation expressions
- •Simple assignment expressions
- •&& expressions
- •|| expressions
- •! expressions
- •?: expressions
- •Anonymous method expressions
- •Yield statements
- •Variable references
- •Atomicity of variable references
- •Conversions
- •Implicit conversions
- •Identity conversion
- •Implicit numeric conversions
- •Implicit enumeration conversions
- •Implicit reference conversions
- •Boxing conversions
- •Implicit type parameter conversions
- •Implicit constant expression conversions
- •User-defined implicit conversions
- •Explicit conversions
- •Explicit numeric conversions
- •Explicit enumeration conversions
- •Explicit reference conversions
- •Unboxing conversions
- •User-defined explicit conversions
- •Standard conversions
- •Standard implicit conversions
- •Standard explicit conversions
- •User-defined conversions
- •Permitted user-defined conversions
- •Evaluation of user-defined conversions
- •User-defined implicit conversions
- •User-defined explicit conversions
- •Anonymous method conversions
- •Method group conversions
- •Expressions
- •Expression classifications
- •Values of expressions
- •Operators
- •Operator precedence and associativity
- •Operator overloading
- •Unary operator overload resolution
- •Binary operator overload resolution
- •Candidate user-defined operators
- •Numeric promotions
- •Unary numeric promotions
- •Binary numeric promotions
- •Member lookup
- •Base types
- •Function members
- •Argument lists
- •Overload resolution
- •Applicable function member
- •Better function member
- •Better conversion
- •Function member invocation
- •Invocations on boxed instances
- •Primary expressions
- •Literals
- •Simple names
- •Invariant meaning in blocks
- •Parenthesized expressions
- •Member access
- •Identical simple names and type names
- •Invocation expressions
- •Method invocations
- •Delegate invocations
- •Element access
- •Array access
- •Indexer access
- •This access
- •Base access
- •Postfix increment and decrement operators
- •The new operator
- •Object creation expressions
- •Array creation expressions
- •Delegate creation expressions
- •The typeof operator
- •The checked and unchecked operators
- •Default value expression
- •Anonymous methods
- •Anonymous method signatures
- •Anonymous method blocks
- •Outer variables
- •Captured outer variables
- •Instantiation of local variables
- •Anonymous method evaluation
- •Implementation example
- •Unary expressions
- •Unary plus operator
- •Unary minus operator
- •Logical negation operator
- •Bitwise complement operator
- •Prefix increment and decrement operators
- •Cast expressions
- •Arithmetic operators
- •Multiplication operator
- •Division operator
- •Remainder operator
- •Addition operator
- •Subtraction operator
- •Shift operators
- •Relational and type-testing operators
- •Integer comparison operators
- •Floating-point comparison operators
- •Decimal comparison operators
- •Boolean equality operators
- •Enumeration comparison operators
- •Reference type equality operators
- •String equality operators
- •Delegate equality operators
- •The is operator
- •The as operator
- •Logical operators
- •Integer logical operators
- •Enumeration logical operators
- •Boolean logical operators
- •Conditional logical operators
- •Boolean conditional logical operators
- •User-defined conditional logical operators
- •Conditional operator
- •Assignment operators
- •Simple assignment
- •Compound assignment
- •Event assignment
- •Expression
- •Constant expressions
- •Boolean expressions
- •Statements
- •End points and reachability
- •Blocks
- •Statement lists
- •The empty statement
- •Labeled statements
- •Declaration statements
- •Local variable declarations
- •Local constant declarations
- •Expression statements
- •Selection statements
- •The if statement
- •The switch statement
- •Iteration statements
- •The while statement
- •The do statement
- •The for statement
- •The foreach statement
- •Jump statements
- •The break statement
- •The continue statement
- •The goto statement
- •The return statement
- •The throw statement
- •The try statement
- •The checked and unchecked statements
- •The lock statement
- •The using statement
- •The yield statement
- •Namespaces
- •Compilation units
- •Namespace declarations
- •Extern alias directives
- •Using directives
- •Using alias directives
- •Using namespace directives
- •Namespace members
- •Type declarations
- •Qualified alias member
- •Classes
- •Class declarations
- •Class modifiers
- •Abstract classes
- •Sealed classes
- •Static classes
- •Class base specification
- •Base classes
- •Interface implementations
- •Class body
- •Partial declarations
- •Class members
- •Inheritance
- •The new modifier
- •Access modifiers
- •Constituent types
- •Static and instance members
- •Nested types
- •Fully qualified name
- •Declared accessibility
- •Hiding
- •this access
- •Reserved member names
- •Member names reserved for properties
- •Member names reserved for events
- •Member names reserved for indexers
- •Member names reserved for destructors
- •Constants
- •Fields
- •Static and instance fields
- •Readonly fields
- •Using static readonly fields for constants
- •Versioning of constants and static readonly fields
- •Volatile fields
- •Field initialization
- •Variable initializers
- •Static field initialization
- •Instance field initialization
- •Methods
- •Method parameters
- •Value parameters
- •Reference parameters
- •Output parameters
- •Parameter arrays
- •Static and instance methods
- •Virtual methods
- •Override methods
- •Sealed methods
- •Abstract methods
- •External methods
- •Method body
- •Method overloading
- •Properties
- •Static and instance properties
- •Accessors
- •Virtual, sealed, override, and abstract accessors
- •Events
- •Field-like events
- •Event accessors
- •Static and instance events
- •Virtual, sealed, override, and abstract accessors
- •Indexers
- •Indexer overloading
- •Operators
- •Unary operators
- •Binary operators
- •Conversion operators
- •Instance constructors
- •Constructor initializers
- •Instance variable initializers
- •Constructor execution
- •Default constructors
- •Private constructors
- •Optional instance constructor parameters
- •Static constructors
- •Destructors
- •Structs
- •Struct declarations
- •Struct modifiers
- •Struct interfaces
- •Struct body
- •Struct members
- •Class and struct differences
- •Value semantics
- •Inheritance
- •Assignment
- •Default values
- •Boxing and unboxing
- •Meaning of this
- •Field initializers
- •Constructors
- •Destructors
- •Static constructors
- •Struct examples
- •Database integer type
- •Database boolean type
- •Arrays
- •Array types
- •The System.Array type
- •Array creation
- •Array element access
- •Array members
- •Array covariance
- •Arrays and the generic IList interface
- •Array initializers
- •Interfaces
- •Interface declarations
- •Interface modifiers
- •Base interfaces
- •Interface body
- •Interface members
- •Interface methods
- •Interface properties
- •Interface events
- •Interface indexers
- •Interface member access
- •Fully qualified interface member names
- •Interface implementations
- •Explicit interface member implementations
- •Interface mapping
- •Interface implementation inheritance
- •Interface re-implementation
- •Abstract classes and interfaces
- •Enums
- •Enum declarations
- •Enum modifiers
- •Enum members
- •The System.Enum type
- •Enum values and operations
- •Delegates
- •Delegate declarations
- •Delegate instantiation
- •Delegate invocation
- •Exceptions
- •Causes of exceptions
- •The System.Exception class
- •How exceptions are handled
- •Common Exception Classes
- •Attributes
- •Attribute classes
- •Attribute usage
- •Positional and named parameters
- •Attribute parameter types
- •Attribute specification
- •Attribute instances
- •Compilation of an attribute
- •Run-time retrieval of an attribute instance
- •Reserved attributes
- •The AttributeUsage attribute
- •The Conditional attribute
- •Conditional Methods
- •Conditional Attribute Classes
- •The Obsolete attribute
- •Unsafe code
- •Unsafe contexts
- •Pointer types
- •Fixed and moveable variables
- •Pointer conversions
- •Pointers in expressions
- •Pointer indirection
- •Pointer member access
- •Pointer element access
- •The address-of operator
- •Pointer increment and decrement
- •Pointer arithmetic
- •Pointer comparison
- •The sizeof operator
- •The fixed statement
- •Stack allocation
- •Dynamic memory allocation
- •Generics
- •Generic class declarations
- •Type parameters
- •The instance type
- •Members of generic classes
- •Static fields in generic classes
- •Static constructors in generic classes
- •Accessing protected members
- •Overloading in generic classes
- •Parameter array methods and type parameters
- •Overriding and generic classes
- •Operators in generic classes
- •Nested types in generic classes
- •Generic struct declarations
- •Generic interface declarations
- •Uniqueness of implemented interfaces
- •Explicit interface member implementations
- •Generic delegate declarations
- •Constructed types
- •Type arguments
- •Open and closed types
- •Base classes and interfaces of a constructed type
- •Members of a constructed type
- •Accessibility of a constructed type
- •Conversions
- •Using alias directives
- •Generic methods
- •Generic method signatures
- •Virtual generic methods
- •Calling generic methods
- •Inference of type arguments
- •Using a generic method with a delegate
- •Constraints
- •Satisfying constraints
- •Member lookup on type parameters
- •Type parameters and boxing
- •Conversions involving type parameters
- •Iterators
- •Iterator blocks
- •Enumerator interfaces
- •Enumerable interfaces
- •Yield type
- •This access
- •Enumerator objects
- •The MoveNext method
- •The Current property
- •The Dispose method
- •Enumerable objects
- •The GetEnumerator method
- •Implementation example
- •Lexical grammar
- •Line terminators
- •White space
- •Comments
- •Unicode character escape sequences
- •Identifiers
- •Keywords
- •Literals
- •Operators and punctuators
- •Pre-processing directives
- •Syntactic grammar
- •Basic concepts
- •Types
- •Expressions
- •Statements
- •Classes
- •Structs
- •Arrays
- •Interfaces
- •Enums
- •Delegates
- •Attributes
- •Generics
- •Grammar extensions for unsafe code
- •Undefined behavior
- •Implementation-defined behavior
- •Unspecified behavior
- •Other Issues
- •Capitalization styles
- •Pascal casing
- •Camel casing
- •All uppercase
- •Capitalization summary
- •Word choice
- •Namespaces
- •Classes
- •Interfaces
- •Enums
- •Static fields
- •Parameters
- •Methods
- •Properties
- •Events
- •Case sensitivity
- •Avoiding type name confusion
- •Documentation Comments
- •Introduction
- •Recommended tags
- •<code>
- •<example>
- •<exception>
- •<list>
- •<para>
- •<param>
- •<paramref>
- •<permission>
- •<remarks>
- •<returns>
- •<seealso>
- •<summary>
- •<value>
- •Processing the documentation file
- •ID string format
- •ID string examples
- •An example
- •C# source code
- •Resulting XML
Chapter 9 Lexical structure
1 |
whitespace:: |
2 |
whitespace-characters |
3 |
whitespace-characters:: |
4 |
whitespace-character |
5 |
whitespace-characters whitespace-character |
6 |
whitespace-character:: |
7 |
Any character with Unicode class Zs |
8 |
Horizontal tab character (U+0009) |
9 |
Vertical tab character (U+000B) |
10 |
Form feed character (U+000C) |
119.4 Tokens
12There are several kinds of tokens: identifiers, keywords, literals, operators, and punctuators. White space
13and comments are not tokens, though they act as separators for tokens.
14token::
15
16
17
18
19
20
21
identifier keyword integer-literal real-literal character-literal string-literal
operator-or-punctuator
229.4.1 Unicode escape sequences
23A Unicode escape sequence represents a Unicode character. Unicode escape sequences are processed in
24identifiers (§9.4.2), regular string literals (§9.4.4.5), and character literals (§9.4.4.4). A Unicode character
25escape is not processed in any other location (for example, to form an operator, punctuator, or keyword).
26unicode-escape-sequence::
27 |
\u |
hex-digit |
hex-digit |
hex-digit |
hex-digit |
28 |
\U |
hex-digit |
hex-digit |
hex-digit |
hex-digit hex-digit hex-digit hex-digit hex-digit |
29A Unicode escape sequence represents the single Unicode character formed by the hexadecimal number
30following the “\u” or “\U” characters. Since C# uses a 16-bit encoding of Unicode characters in characters
31and string values, a Unicode code point in the range U+10000 to U+10FFFF is represented using two
32Unicode surrogate code units. Unicode code points above 0x10FFFF are invalid and are not supported.
33Multiple translations are not performed. For instance, the string literal “\u005Cu005C” is equivalent to
34“\u005C” rather than “\”. [Note: The Unicode value \u005C is the character “\”. end note]
35[Example: The example
36class Class1
37{
38 |
static void Test(bool \u0066) { |
39 |
char c = '\u0066'; |
40 |
if (\u0066) |
41 |
System.Console.WriteLine(c.ToString()); |
42}
43}
44shows several uses of \u0066, which is the escape sequence for the letter “f”. The program is equivalent to
67
C# LANGUAGE SPECIFICATION
1class Class1
2{
3 |
static void Test(bool f) { |
4 |
char c = 'f'; |
5 |
if (f) |
6 |
System.Console.WriteLine(c.ToString()); |
7}
8}
9end example]
109.4.2 Identifiers
11The rules for identifiers given in this subclause correspond exactly to those recommended by the Unicode
12Standard Annex 15 except that underscore is allowed as an initial character (as is traditional in the
13C programming language), Unicode escape sequences are permitted in identifiers, and the “@” character is
14allowed as a prefix to enable keywords to be used as identifiers.
15identifier::
16 |
available-identifier |
17@ identifier-or-keyword
18available-identifier::
19 |
An identifier-or-keyword that is not a keyword |
20 |
identifier-or-keyword:: |
21 |
identifier-start-character identifier-part-charactersopt |
22 |
identifier-start-character:: |
23 |
letter-character |
24_ (the underscore character U+005F)
25identifier-part-characters::
26 |
identifier-part-character |
27 |
identifier-part-characters identifier-part-character |
28 |
identifier-part-character:: |
29 |
letter-character |
30 |
decimal-digit-character |
31 |
connecting-character |
32 |
combining-character |
33 |
formatting-character |
34 |
letter-character:: |
35 |
A Unicode character of classes Lu, Ll, Lt, Lm, Lo, or Nl |
36 |
A unicode-escape-sequence representing a character of classes Lu, Ll, Lt, Lm, Lo, or Nl |
37 |
combining-character:: |
38 |
A Unicode character of classes Mn or Mc |
39 |
A unicode-escape-sequence representing a character of classes Mn or Mc |
40 |
decimal-digit-character:: |
41 |
A Unicode character of the class Nd |
42 |
A unicode-escape-sequence representing a character of the class Nd |
43 |
connecting-character:: |
44 |
A Unicode character of the class Pc |
45 |
A unicode-escape-sequence representing a character of the class Pc |
46 |
formatting-character:: |
47 |
A Unicode character of the class Cf |
48 |
A unicode-escape-sequence representing a character of the class Cf |
68
Chapter 9 Lexical structure
1[Note: For information on the Unicode character classes mentioned above, see The Unicode Standard,
2Verson 3.0, §4.5. end note]
3[Example: Examples of valid identifiers include “identifier1”, “_identifier2”, and “@if”. end
4example]
5An identifier in a conforming program shall be in the canonical format defined by Unicode Normalization
6Form C, as defined by Unicode Standard Annex 15. The behavior when encountering an identifier not in
7Normalization Form C is implementation-defined; however, a diagnostic is not required.
8The prefix “@” enables the use of keywords as identifiers, which is useful when interfacing with other
9programming languages. The character @ is not actually part of the identifier, so the identifier might be seen
10in other languages as a normal identifier, without the prefix. An identifier with an @ prefix is called a
11verbatim identifier. [Note: Use of the @ prefix for identifiers that are not keywords is permitted, but strongly
12discouraged as a matter of style. end note]
13[Example: The example:
14class @class
15{
16 |
public static void @static(bool @bool) { |
17 |
if (@bool) |
18 |
System.Console.WriteLine("true"); |
19 |
else |
20 |
System.Console.WriteLine("false"); |
21}
22}
23class Class1
24{
25 |
static void M() { |
26 |
cl\u0061ss.st\u0061tic(true); |
27}
28}
29defines a class named “class” with a static method named “static” that takes a parameter named
30“bool”. Note that since Unicode escapes are not permitted in keywords, the token “cl\u0061ss” is an
31identifier, and is the same identifier as “@class”. end example]
32Two identifiers are considered the same if they are identical after the following transformations are applied,
33in order:
34• The prefix “@”, if used, is removed.
35• Each unicode-escape-sequence is transformed into its corresponding Unicode character.
36• Any formatting-characters are removed.
37Identifiers containing two consecutive underscore characters (U+005F) are reserved for use by the
38implementation; however, no diagnostic is required if such an identifier is defined. [Note: For example, an
39implementation might provide extended keywords that begin with two underscores. end note]
409.4.3 Keywords
41A keyword is an identifier-like sequence of characters that is reserved, and cannot be used as an identifier
42except when prefaced by the @ character.
69