5.1 Creating Interfaces
Classes and Objects in Guide: Racket introduces classes, objects, and interfaces.
(interface (super-interface-expr ...) id ...) |
Produces an interface. The ids must be mutually distinct.
Each super-interface-expr is evaluated (in order) when the
interface expression is evaluated. The result of each
super-interface-expr must be an interface value, otherwise
the exn:fail:object exception is raised. The interfaces returned by the
super-interface-exprs are the new interface’s
superinterfaces, which are all extended by the new interface. Any
class that implements the new interface also implements all of the
superinterfaces.
The result of an interface expression is an interface that
includes all of the specified ids, plus all identifiers from
the superinterfaces. Duplicate identifier names among the
superinterfaces are ignored, but if a superinterface contains one of
the ids in the interface expression, the
exn:fail:object exception is raised.
If no super-interface-exprs are provided, then the derivation
requirement of the resulting interface is trivial: any class that
implements the interface must be derived from object%.
Otherwise, the implementation requirement of the resulting interface
is the most specific requirement from its superinterfaces. If the
superinterfaces specify inconsistent derivation requirements, the
exn:fail:object exception is raised.
Examples: |
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(define directory-interface | (interface (file-interface) file-list parent-directory)) | |
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(interface* (super-interface-expr ...) | ([property-expr val-expr] ...) | id ...) |
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Like
interface, but also associates to the interface the
structure-type properties produced by the
property-exprs with
the corresponding
val-exprs.
Whenever the resulting interface (or a sub-interface derived from it)
is explicitly implemented by a class through the class* form,
each property is attached with its value to a structure type that
instantiated by instances of the class. Specifically, the property is
attached to a structure type with zero immediate fields, which is
extended to produce the internal structure type for instances of the
class (so that no information about fields is accessible to the
structure type property’s guard, if any).