5.4 Field and Method Access
In expressions within a class definition, the initialization variables, fields, and methods of the class all part of the environment. Within a method body, only the fields and other methods of the class can be referenced; a reference to any other class-introduced identifier is a syntax error. Elsewhere within the class, all class-introduced identifiers are available, and fields and initialization variables can be mutated with set!.
5.4.1 Methods
Method names within a class can only be used in the procedure position of an application expression; any other use is a syntax error.
To allow methods to be applied to lists of arguments, a method application can have the following form:
(method-id arg ... . arg-list-expr)
This form calls the method in a way analogous to (apply method-id arg ... arg-list-expr). The arg-list-expr must not be a parenthesized expression.
Methods are called from outside a class with the send and send/apply forms.
If obj-expr does not produce an object, the exn:fail:contract exception is raised. If the object has no public method named method-id, the exn:fail:object exception is raised.
(send/apply obj-expr method-id arg ... arg-list-expr) |
(send* obj-expr msg ...) | ||||||||||
|
For example,
(send* edit (begin-edit-sequence) |
(insert "Hello") |
(insert #\newline) |
(end-edit-sequence)) |
is the same as
(let ([o edit]) |
(send o begin-edit-sequence) |
(send o insert "Hello") |
(send o insert #\newline) |
(send o end-edit-sequence)) |
|
Example:
(let ([s (new stack%)]) |
(with-method ([push (s push!)] |
[pop (s pop!)]) |
(push 10) |
(push 9) |
(pop))) |
is the same as
(let ([s (new stack%)]) |
(send s push! 10) |
(send s push! 9) |
(send s pop!)) |
5.4.2 Fields
(get-field id obj-expr) |
If obj-expr does not produce an object, the exn:fail:contract exception is raised. If the object has no id method, the exn:fail:object exception is raised.
(set-field! id obj-expr expr) |
If obj-expr does not produce an object, the exn:fail:contract exception is raised. If the object has no id method, the exn:fail:object exception is raised.
(field-bound? id obj-expr) |
If obj-expr does not produce an object, the exn:fail:contract exception is raised.
(class-field-accessor class-expr field-id) |
If class-expr does not produce a class, the exn:fail:contract exception is raised. If the class has no field-id field, the exn:fail:object exception is raised.
(class-field-mutator class-expr field-id) |
If class-expr does not produce a class, the exn:fail:contract exception is raised. If the class has no field-id field, the exn:fail:object exception is raised.
5.4.3 Generics
A generic can be used instead of a method name to avoid the cost of relocating a method by name within a class.
(generic class-or-interface-expr id) |
If class-or-interface-expr does not produce a class or interface, the exn:fail:contract exception is raised. If the resulting class or interface does not contain a method named id, the exn:fail:object exception is raised.
(send-generic obj-expr generic-expr arg ...) |
(send-generic obj-expr generic-expr arg ... . arg-list-expr) |
If obj-expr does not produce a object, or if generic-expr does not produce a generic, the exn:fail:contract exception is raised. If the result of obj-expr is not an instance of the class or interface encapsulated by the result of generic-expr, the exn:fail:object exception is raised.
(make-generic type method-name) → generic? |
type : (or/c class? interface?) |
method-name : symbol? |