Language Specification Version 0 Notice

13.1.1Interface modifiers

It is a compile-time error for the same modifier to appear multiple times in an interface declaration.

The new modifier is only permitted on interfaces defined within a class. It specifies that the interface hides an inherited member by the same name, as described in §10.3.4.

The public, protected, internal, and private modifiers control the accessibility of the interface. Depending on the context in which the interface declaration occurs, only some of these modifiers may be permitted (§3.5.1).

13.1.2Partial modifier

13.1.3Base interfaces

For a constructed interface type, the explicit base interfaces are formed by taking the explicit base interface declarations on the generic type declaration, and substituting, for each type-parameter in the base interface declaration, the corresponding type-argument of the constructed type.

The explicit base interfaces of an interface must be at least as accessible as the interface itself (§3.5.4). For example, it is a compile-time error to specify a private or internal interface in the interface-base of a public interface.

It is a compile-time error for an interface to directly or indirectly inherit from itself.

The base interfaces of an interface are the explicit base interfaces and their base interfaces. In other words, the set of base interfaces is the complete transitive closure of the explicit base interfaces, their explicit base interfaces, and so on. An interface inherits all members of its base interfaces. In the example

interface IControl

interface ITextBox: IControl

interface IListBox: IControl

interface IComboBox: ITextBox, IListBox {}

the base interfaces of IComboBox are IControl, ITextBox, and IListBox.

In other words, the IComboBox interface above inherits members SetText and SetItems as well as Paint.

A class or struct that implements an interface also implicitly implements all of the interface’s base interfaces.

13.1.4Interface body

13.2Interface members

An interface declaration may declare zero or more members. The members of an interface must be methods, properties, events, or indexers. An interface cannot contain constants, fields, operators, instance constructors, destructors, or types, nor can an interface contain static members of any kind.

All interface members implicitly have public access. It is a compile-time error for interface member declarations to include any modifiers. In particular, interfaces members cannot be declared with the modifiers abstract, public, protected, internal, private, virtual, override, or static.

The example

public delegate void StringListEvent(IStringList sender);

public interface IStringList

int Count { get; }

event StringListEvent Changed;

string this[int index] { get; set; }

declares an interface that contains one each of the possible kinds of members: A method, a property, an event, and an indexer.

An interface-declaration creates a new declaration space (§3.3), and the interface-member-declarations immediately contained by the interface-declaration introduce new members into this declaration space. The following rules apply to interface-member-declarations:

• 
  The name of a method must differ from the names of all properties and events declared in the same interface. In addition, the signature (§3.6) of a method must differ from the signatures of all other methods declared in the same interface, and two methods declared in the same interface may not have signatures that differ solely by ref and out.
  
• 
  The name of a property or event must differ from the names of all other members declared in the same interface.
  
• 
  The signature of an indexer must differ from the signatures of all other indexers declared in the same interface.
  

If a new modifier is included in a declaration that doesn’t hide an inherited member, a warning is issued to that effect. This warning is suppressed by removing the new modifier.

Note that the members in class object are not, strictly speaking, members of any interface (§13.2). However, the members in class object are available via member lookup in any interface type (§7.3).

13.2.1Interface methods

The attributes, return-type, identifier, and formal-parameter-list of an interface method declaration have the same meaning as those of a method declaration in a class (§10.6). An interface method declaration is not permitted to specify a method body, and the declaration therefore always ends with a semicolon.

13.2.2Interface properties

Interface properties are declared using interface-property-declarations:

interface-property-declaration:
attributes_opt new_opt type identifier { interface-accessors }

interface-accessors:
attributes_opt get ;
attributes_opt set ;
attributes_opt get ; attributes_opt set ;
attributes_opt set ; attributes_opt get ;

The attributes, type, and identifier of an interface property declaration have the same meaning as those of a property declaration in a class (§10.7).

The accessors of an interface property declaration correspond to the accessors of a class property declaration (§10.7.2), except that the accessor body must always be a semicolon. Thus, the accessors simply indicate whether the property is read-write, read-only, or write-only.

13.2.3Interface events

Interface events are declared using interface-event-declarations:

interface-event-declaration:
attributes_opt new_opt event type identifier ;

The attributes, type, and identifier of an interface event declaration have the same meaning as those of an event declaration in a class (§10.8).

13.2.4Interface indexers

Interface indexers are declared using interface-indexer-declarations:

interface-indexer-declaration:
attributes_opt new_opt type this [ formal-parameter-list ] { interface-accessors }

The attributes, type, and formal-parameter-list of an interface indexer declaration have the same meaning as those of an indexer declaration in a class (§10.9).

The accessors of an interface indexer declaration correspond to the accessors of a class indexer declaration (§10.9), except that the accessor body must always be a semicolon. Thus, the accessors simply indicate whether the indexer is read-write, read-only, or write-only.

13.2.5Interface member access

Interface members are accessed through member access (§7.5.4) and indexer access (§7.5.6.2) expressions of the form I.M and I[A], where I is an interface type, M is a method, property, or event of that interface type, and A is an indexer argument list.

For interfaces that are strictly single-inheritance (each interface in the inheritance chain has exactly zero or one direct base interface), the effects of the member lookup (§7.3), method invocation (§7.5.5.1), and indexer access (§7.5.6.2) rules are exactly the same as for classes and structs: More derived members hide less derived members with the same name or signature. However, for multiple-inheritance interfaces, ambiguities can occur when two or more unrelated base interfaces declare members with the same name or signature. This section shows several examples of such situations. In all cases, explicit casts can be used to resolve the ambiguities.

In the example

interface IList

{
int Count { get; set; }
}

interface ICounter

{
void Count(int i);
}

interface IListCounter: IList, ICounter {}

class C
{
void Test(IListCounter x) {
x.Count(1); // Error
x.Count = 1; // Error
((IList)x).Count = 1; // Ok, invokes IList.Count.set
((ICounter)x).Count(1); // Ok, invokes ICounter.Count
}
}

the first two statements cause compile-time errors because the member lookup (§7.3) of Count in IListCounter is ambiguous. As illustrated by the example, the ambiguity is resolved by casting x to the appropriate base interface type. Such casts have no run-time costs—they merely consist of viewing the instance as a less derived type at compile-time.

In the example

interface IInteger

{
void Add(int i);
}

interface IDouble

{
void Add(double d);
}

interface INumber: IInteger, IDouble {}

class C
{
void Test(INumber n) {
n.Add(1); // Invokes IInteger.Add
n.Add(1.0); // Only IDouble.Add is applicable
((IInteger)n).Add(1); // Only IInteger.Add is a candidate
((IDouble)n).Add(1); // Only IDouble.Add is a candidate
}
}

the invocation n.Add(1) selects IInteger.Add by applying the overload resolution rules of §7.4.3. Similarly the invocation n.Add(1.0) selects IDouble.Add. When explicit casts are inserted, there is only one candidate method, and thus no ambiguity.

In the example

interface IBase

{
void F(int i);
}

interface ILeft: IBase

{
new void F(int i);
}

interface IRight: IBase

{
void G();
}

interface IDerived: ILeft, IRight {}

class A
{
void Test(IDerived d) {
d.F(1); // Invokes ILeft.F
((IBase)d).F(1); // Invokes IBase.F
((ILeft)d).F(1); // Invokes ILeft.F
((IRight)d).F(1); // Invokes IBase.F
}
}

the IBase.F member is hidden by the ILeft.F member. The invocation d.F(1) thus selects ILeft.F, even though IBase.F appears to not be hidden in the access path that leads through IRight.

The intuitive rule for hiding in multiple-inheritance interfaces is simply this: If a member is hidden in any access path, it is hidden in all access paths. Because the access path from IDerived to ILeft to IBase hides IBase.F, the member is also hidden in the access path from IDerived to IRight to IBase.

Directory: download
download -> Performance Tuning Guidelines for Windows Server 2008 May 20, 2009 Abstract
download -> Northern England’s set-jetting locations
download -> Bbc archives: Beyond the programme download
download -> Occupational health and safety
download -> Dynatest 3031 lwd light Weight Deflectometer
download -> Forth coming competitive exams
download -> English Olympiad Tasks: 10 th form Аудіювання, 10 клас. Текст
download -> Brush High School Morning Announcements Friday, September 05, 2014 all school
download -> Year 9 The Arts — Music
download -> Years 7 and 8 standard elaborations — Australian Curriculum: Music draft

Download 3.2 Mb.

Share with your friends: