- •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 14 Expressions
114.5.4.1 Identical simple names and type names
2In a member access of the form E.I, if E is a single identifier, and if the meaning of E as a simple-name
3(§14.5.2) is a constant, field, property, local variable, or parameter with the same type as the meaning of E as
4a type-name (§10.8), then both possible meanings of E are permitted. The two possible meanings of E.I are
5never ambiguous, since I shall necessarily be a member of the type E in both cases. In other words, the rule
6simply permits access to the static members and nested types of E where a compile-time error would
7otherwise have occurred. [Example:
8struct Color
9{
10 |
public |
static |
readonly |
Color |
White |
= |
new |
Color(…); |
11 |
public |
static |
readonly |
Color |
Black |
= |
new |
Color(…); |
12public Color Complement() {…}
13}
14class A
15{
16 |
public Color Color; |
// Field A.Color of type Color |
17 |
void F() { |
|
18 |
Color = Color.Black; |
// References Color.Black |
19 |
Color = Color.Complement(); |
// Invokes Complement() on A.Color |
20 |
} |
|
21 |
static void G() { |
|
22 |
Color c = Color.White; |
// References Color.White |
23}
24}
25Within the A class, those occurrences of the Color identifier that reference the Color type are underlined,
26and those that reference the Color field are not underlined. end example]
2714.5.5 Invocation expressions
28An invocation-expression is used to invoke a method.
29invocation-expression:
30 |
primary-expression ( argument-listopt ) |
31The primary-expression of an invocation-expression shall be a method group or a value of a delegate-type. If
32the primary-expression is a method group, the invocation-expression is a method invocation (§14.5.5.1). If
33the primary-expression is a value of a delegate-type, the invocation-expression is a delegate invocation
34(§14.5.5.2). If the primary-expression is neither a method group nor a value of a delegate-type, a compile-
35time error occurs.
36The optional argument-list (§14.4.1) provides values or variable references for the parameters of the method.
37The result of evaluating an invocation-expression is classified as follows:
38• If the invocation-expression invokes a method or delegate that returns void, the result is nothing. An
39expression that is classified as nothing cannot be an operand of any operator, and is permitted only in the
40context of a statement-expression (§15.6).
41• Otherwise, the result is a value of the type returned by the method or delegate.
4214.5.5.1 Method invocations
43For a method invocation, the primary-expression of the invocation-expression shall be a method group. The
44method group identifies the one method to invoke or the set of overloaded methods from which to choose a
45specific method to invoke. In the latter case, determination of the specific method to invoke is based on the
46context provided by the types of the arguments in the argument-list.
47The compile-time processing of a method invocation of the form M(A), where M is a method group (possibly
48including a type-argument-list), and A is an optional argument-list, consists of the following steps:
165
C# LANGUAGE SPECIFICATION
1• The set of candidate methods for the method invocation is constructed. For each method F associated
2with the method group M:
3o If F is non-generic, F is a candidate when:
4• M has no type argument list, and
5• F is applicable with respect to A (§14.4.2.1).
6o If F is generic and M has no type argument list, F is a candidate when:
7• Type inference (§26.6.4) succeeds, inferring a list of type arguments for the call, and
8• Once the inferred type arguments are substituted for the corresponding method type parameters,
9 |
the parameter list of F is applicable with respect to A (§14.4.2.1), and |
10 |
• The parameter list of F, after substituting type arguments, is not the same as an applicable non- |
11 |
generic method, possibly in expanded form (§14.4.2.1), declared in the same type as F. |
12o If F is generic and M includes a type argument list, F is a candidate when:
13• F has the same number of method type parameters as were supplied in the type argument list,
14 |
and |
15 |
• Once the type arguments are substituted for the corresponding method type parameters, the |
16 |
parameter list of F is applicable with respect to A (§14.4.2.1). |
17• The set of candidate methods is reduced to contain only methods from the most derived types: For each
18method C.F in the set, where C is the type in which the method F is declared, all methods declared in a
19base type of C are removed from the set. Furthermore, if C is a class type other than object, all methods
20declared in an interface type are removed from the set. [Note: This latter rule only has affect when the
21method group was the result of a member lookup on a type parameter having an effective base class
22other than object and a non-empty effective interface set (§26.7). end note]
23• If the resulting set of candidate methods is empty, then no applicable methods exist, and a compile-time
24error occurs. If the candidate methods are not all declared in the same type, the method invocation is
25ambiguous, and a compile-time error occurs (this latter situation can only occur for an invocation of a
26method in an interface that has multiple direct base interfaces, as described in §20.2.5, or for an
27invocation of a method on a type parameter).
28• The best method of the set of candidate methods is identified using the overload resolution rules of
29§14.4.2. If a single best method cannot be identified, the method invocation is ambiguous, and a
30compile-time error occurs. When performing overload resolution, the parameters of a generic method
31are considered after substituting the type arguments (supplied or inferred) for the corresponding method
32type parameters.
33• Final validation of the chosen best method is performed:
34o The method is validated in the context of the method group: If the best method is a static method,
35the method group shall have resulted from a simple-name or a member-access through a type. If the
36best method is an instance method, the method group shall have resulted from a simple-name, a
37member-access through a variable or value, or a base-access. If neither of these requirements is true,
38a compile-time error occurs.
39o If the best method is a generic method, the type arguments (supplied or inferred) are checked against
40the constraints (§26.7.1) declared on the generic method. If any type argument does not satisfy the
41corresponding constraint(s) on the type parameter, a compile-time error occurs.
42Once a method has been selected and validated at compile-time by the above steps, the actual run-time
43invocation is processed according to the rules of function member invocation described in §14.4.3.
44[Note: The intuitive effect of the resolution rules described above is as follows: To locate the particular
45method invoked by a method invocation, start with the type indicated by the method invocation and proceed
166