Interface-Oriented Programming for Classes

7.7

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Interface-Oriented Programming for Classes

syntax
(define-interface name-id (super-ifc-id ...) (method-id ...))

Defines name-id as a static interface extending the interfaces named by the super-ifc-ids and containing the methods specified by the method-ids.

A static interface name is used by the checked method call variants (send/i, send*/i, and send/apply/i). When used as an expression, a static interface name evaluates to an interface value.

Examples:

> (define-interface stack<%> () (empty? push pop))
> stack<%>
#<interface:stack<%>>
> (define stack%
    (class* object% (stack<%>)
      (define items null)
      (define/public (empty?) (null? items))
      (define/public (push x) (set! items (cons x items)))
      (define/public (pop) (begin (car items) (set! items (cdr items))))
      (super-new)))

syntax
(define-interface/dynamic name-id ifc-expr (method-id ...))

Defines name-id as a static interface with dynamic counterpart ifc-expr, which must evaluate to an interface value. The static interface contains the methods named by the method-ids. A run-time error is raised if any method-id is not a member of the dynamic interface ifc-expr.

Use define-interface/dynamic to wrap interfaces from other sources.

Examples:

> (define-interface/dynamic object<%> (class->interface object%) ())
> object<%>
#<interface:object%>

syntax
(send/i obj-exp static-ifc-id method-id arg-expr ...)

Checked variant of send.

The argument static-ifc-id must be defined as a static interface. The method method-id must be a member of the static interface static-ifc-id; otherwise a compile-time error is raised.

The value of obj-expr must be an instance of the interface static-ifc-id; otherwise, a run-time error is raised.

Examples:

> (define s (new stack%))
> (send/i s stack<%> push 1)
> (send/i s stack<%> popp)
eval:9:0: send/i: method not in static interface
in: popp
> (send/i (new object%) stack<%> push 2)
send/i: interface check failed on: (object)

syntax
(send*/i obj-expr static-ifc-id (method-id arg-expr ...) ...)

Checked variant of send*.

Example:

> (send*/i s stack<%>
(push 2)
(pop))

syntax
(send/apply/i obj-expr static-ifc-id method-id arg-expr ... list-arg-expr)

Checked variant of send/apply.

Example:

> (send/apply/i s stack<%> push (list 5))

syntax
(define/i id static-ifc-id expr)

Checks that expr evaluates to an instance of static-ifc-id before binding it to id. If id is subsequently changed (with set!), the check is performed again.

No dynamic object check is performed when calling a method (using send/i, etc) on a name defined via define/i.

syntax
(init/i (id static-ifc-id maybe-default-expr) ...)
syntax
(init-field/i (id static-ifc-id maybe-default-expr) ...)
syntax
(init-private/i (id static-ifc-id maybe-default-expr) ...)

maybe-default-expr = ()
| default-expr

Checked versions of init and init-field. The value attached to each id is checked against the given interface.

No dynamic object check is performed when calling a method (using send/i, etc) on a name bound via one of these forms. Note that in the case of init-field/i this check omission is unsound in the presence of mutation from outside the class. This should be fixed.

syntax
(define-interface-expander id transformer-expr)

Defines id as a macro that can be used within define-interface forms.

Examples:

> (define-interface-expander stack-methods
(lambda (stx) #'[empty? push pop]))
> (define-interface stack<%> ()
((stack-methods)))
> (interface->method-names stack<%>)
'(push empty? pop)

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