- •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
C# LANGUAGE SPECIFICATION
1• Otherwise, the expanded form is applicable if for each argument in A the parameter passing mode of the
2argument is identical to the parameter passing mode of the corresponding parameter, and
3o for a fixed value parameter or a value parameter created by the expansion, an implicit conversion
4(§13.1) exists from the type of the argument to the type of the corresponding parameter, or
5o for a ref or out parameter, the type of the argument is identical to the type of the corresponding
6parameter.
714.4.2.2 Better function member
8Given an argument list A with a set of argument types A1, A2, …, AN and two applicable function members MP
9and MQ with parameter types P1, P2, …, PN and Q1, Q2, …, QN, MP is defined to be a better function member
10than MQ if
11• for each argument, the implicit conversion from AX to PX is not worse than the implicit conversion from
12AX to QX, and
13• for at least one argument, the conversion from AX to PX is better than the conversion from AX to QX.
14When performing this evaluation, if MP or MQ is applicable in its expanded form, then PX or QX refers to a
15parameter in the expanded form of the parameter list.
1614.4.2.3 Better conversion
17Given an implicit conversion C1 that converts from a type S to a type T1, and an implicit conversion C2 that
18converts from a type S to a type T2, the better conversion of the two conversions is determined as follows:
19• If T1 and T2 are the same type, neither conversion is better.
20• If S is T1, C1 is the better conversion.
21• If S is T2, C2 is the better conversion.
22• If an implicit conversion from T1 to T2 exists, and no implicit conversion from T2 to T1 exists, C1 is the
23better conversion.
24• If an implicit conversion from T2 to T1 exists, and no implicit conversion from T1 to T2 exists, C2 is the
25better conversion.
26• If T1 is sbyte and T2 is byte, ushort, uint, or ulong, C1 is the better conversion.
27• If T2 is sbyte and T1 is byte, ushort, uint, or ulong, C2 is the better conversion.
28• If T1 is short and T2 is ushort, uint, or ulong, C1 is the better conversion.
29• If T2 is short and T1 is ushort, uint, or ulong, C2 is the better conversion.
30• If T1 is int and T2 is uint, or ulong, C1 is the better conversion.
31• If T2 is int and T1 is uint, or ulong, C2 is the better conversion.
32• If T1 is long and T2 is ulong, C1 is the better conversion.
33• If T2 is long and T1 is ulong, C2 is the better conversion.
34• Otherwise, neither conversion is better.
35If an implicit conversion C1 is defined by these rules to be a better conversion than an implicit conversion C2,
36then it is also the case that C2 is a worse conversion than C1.
3714.4.3 Function member invocation
38This subclause describes the process that takes place at run-time to invoke a particular function member. It is
39assumed that a compile-time process has already determined the particular member to invoke, possibly by
40applying overload resolution to a set of candidate function members.
158
Chapter 14 Expressions
1For purposes of describing the invocation process, function members are divided into two categories:
2• Static function members. These are static methods, static property accessors, and user-defined operators.
3Static function members are always non-virtual.
4• Instance function members. These are instance methods, instance constructors, instance property
5accessors, and indexer accessors. Instance function members are either non-virtual or virtual, and are
6always invoked on a particular instance. The instance is computed by an instance expression, and it
7becomes accessible within the function member as this (§14.5.7). For an instance constructor, the
8instance expression is taken to be the newly allocated object.
9The run-time processing of a function member invocation consists of the following steps, where M is the
10function member and, if M is an instance member, E is the instance expression:
11• If M is a static function member:
12o The argument list is evaluated as described in §14.4.1.
13o M is invoked.
14• If M is an instance function member declared in a value-type:
15o E is evaluated. If this evaluation causes an exception, then no further steps are executed. For an
16instance constructor, this evaluation consists of allocating the storage (typically from an execution
17stack) for the new object. In this case E is classified as a variable.
18o If E is not classified as a variable, then a temporary local variable of E’s type is created and the value
19of E is assigned to that variable. E is then reclassified as a reference to that temporary local variable.
20The temporary variable is accessible as this within M, but not in any other way. Thus, only when E
21is a true variable is it possible for the caller to observe the changes that M makes to this.
22o The argument list is evaluated as described in §14.4.1.
23o M is invoked. The variable referenced by E becomes the variable referenced by this.
24• If M is an instance function member declared in a reference-type:
25o E is evaluated. If this evaluation causes an exception, then no further steps are executed. For an
26instance constructor, this evaluation consists of allocating (typically from a garbage collected heap)
27the storage for the new object.
28o The argument list is evaluated as described in §14.4.1.
29o If the type of E is a value-type, a boxing conversion (§11.3.1) is performed to convert E to type
30System.Enum (if E is an enum) or System.ValueType, and E is considered to be of this type in
31the following steps. [Note: In this case, M could only be a member of System.Enum,
32System.ValueType, or System.Object. end note]
33o The value of E is checked to be valid. If the value of E is null, a
34System.NullReferenceException is thrown and no further steps are executed.
35o The function member implementation to invoke is determined:
36• If the compile-time type of E is an interface, the function member to invoke is the
37 |
implementation of M provided by the run-time type of the instance referenced by E. This |
38 |
function member is determined by applying the interface mapping rules (§20.4.2). |
39 |
• Otherwise, if M is a virtual function member, the function member to invoke is the |
40 |
implementation of M provided by the run-time type of the instance referenced by E. This |
41 |
function member is determined by applying the rules for determining the most derived |
42 |
implementation (§17.5.3) of M with respect to the run-time type of the instance referenced by E. |
43 |
• Otherwise, M is a non-virtual function member, and the function member to invoke is M itself. |
159