Original
Forward declarations
An interface declaration that ends
with the reserved word interface and a semicolon, without specifying an
ancestor, GUID, or member list, is a forward declaration. A forward
declaration must be resolved by a defining declaration of the same
interface within the same type declaration section. In other words, between a
forward declaration and its defining declaration, nothing can occur except
other type declarations.
Forward declarations allow
mutually dependent interfaces. For example,
type
IControl = interface;
IWindow = interface
['{00000115-0000-0000-C000-000000000044}']
function GetControl(Index: Integer):
IControl;
...
end;
IControl = interface
['{00000115-0000-0000-C000-000000000049}']
function GetWindow: IWindow;
...
end;
Mutually derived interfaces are not allowed. For example, it is not legal to derive IWindow from IControl and also derive IControl from IWindow.
See also
译文
向前声明
接口声明以保留字interface和一个分号结束，没有指定祖先、GUID或成员列表，这样的声明是一个向前声明（forward
declaration）。接口的向前声明必须在相同的类型声明节中被同一接口的定义声明（defining declaration）解析。换句话说，在向前声明极其定义声明之间，除了其他的类型声明之外，不能有任何其他内容。
向前声明允许接口相互依赖。例如，
type
IControl = interface;
IWindow = interface
['{00000115-0000-0000-C000-000000000044}']
function GetControl(Index: Integer):
IControl;
...
end;
IControl = interface
['{00000115-0000-0000-C000-000000000049}']
function GetWindow: IWindow;
...
end;
相互起源的接口是不允许的。例如，IWindow起源于IControl并且IControl又起源于IWindow，这是不合法的。