►The Racket Reference
▼5 Classes and Objects
On this page:
object?
class?
interface?
generic?
object=?
object->vector
class->interface
object-interface
is-a?
subclass?
implementation?
interface-extension?
method-in-interface?
interface->method-names
object-method-arity-includes?
field-names
object-info
class-info
exn: fail: object
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5.11 Object, Class, and Interface Utilities

procedure

(object? v) → boolean?

  v : any/c
Returns #t if v is an object, #f otherwise.

Examples:

> (object? (new object%))

#t

> (object? object%)

#f

> (object? "clam chowder")

#f

procedure

(class? v) → boolean?

  v : any/c
Returns #t if v is a class, #f otherwise.

Examples:

> (class? object%)

#t

> (class? (class object% (super-new)))

#t

> (class? (new object%))

#f

> (class? "corn chowder")

#f

procedure

(interface? v) → boolean?

  v : any/c
Returns #t if v is an interface, #f otherwise.

Examples:

> (interface? (interface () empty cons first rest))

#t

> (interface? object%)

#f

> (interface? "gazpacho")

#f

procedure

(generic? v) → boolean?

  v : any/c
Returns #t if v is a generic, #f otherwise.

Examples:

(define c%
  (class object%
    (super-new)
    (define/public (m x)
      (+ 3.14 x))))
> (generic? (generic c% m))

#t

> (generic? c%)

#f

> (generic? "borscht")

#f

procedure

(object=? a b) → boolean?

  a : object?
  b : object?
Determines if two objects are the same object, or not; this procedure uses eq?, but also works properly with contracts.

Examples:

(define obj-1 (new object%))
> (define/contract obj-2 (object/c) obj-1)
> (object=? obj-1 obj-1)

#t

> (object=? (new object%) obj-1)

#f

> (object=? obj-1 obj-2)

#t

> (object=? obj-1 (new (class object% (super-new))))

#f

procedure

(object->vector object [opaque-v]) → vector?

  object : object?
  opaque-v : any/c = #f
Returns a vector representing object that shows its inspectable fields, analogous to struct->vector.

Examples:

> (object->vector (new object%))

'#(object:object% ...)

> (object->vector (new (class object%
                         (super-new)
                         (field [x 5] [y 10]))))

'#(object:eval:82:0 ...)

procedure

(class->interface class) → interface?

  class : class?
Returns the interface implicitly defined by class.

Example:

> (class->interface object%)

#<interface:object%>

procedure

(object-interface object) → interface?

  object : object?
Returns the interface implicitly defined by the class of object.

Example:

> (object-interface (new object%))

#<interface:object%>

procedure

(is-a? v type) → boolean?

  v : any/c
  type : (or/c interface? class?)
Returns #t if v is an instance of a class type or a class that implements an interface type, #f otherwise.

Examples:

(define point<%> (interface () get-x get-y))
(define 2d-point%
  (class* object% (point<%>)
    (super-new)
    (field [x 0] [y 0])
    (define/public (get-x) x)
    (define/public (get-y) y)))
> (is-a? (new 2d-point%) 2d-point%)

#t

> (is-a? (new 2d-point%) point<%>)

#t

> (is-a? (new object%) 2d-point%)

#f

> (is-a? (new object%) point<%>)

#f

procedure

(subclass? v class) → boolean?

  v : any/c
  class : class?
Returns #t if v is a class derived from (or equal to) class, #f otherwise.

Examples:

> (subclass? (class object% (super-new)) object%)

#t

> (subclass? object% (class object% (super-new)))

#f

> (subclass? object% object%)

#t

procedure

(implementation? v interface) → boolean?

  v : any/c
  interface : interface?
Returns #t if v is a class that implements interface, #f otherwise.

Examples:

(define i<%> (interface () go))
(define c%
  (class* object% (i<%>)
    (super-new)
    (define/public (go) 'go)))
> (implementation? c% i<%>)

#t

> (implementation? object% i<%>)

#f

procedure

(interface-extension? v interface) → boolean?

  v : any/c
  interface : interface?
Returns #t if v is an interface that extends interface, #f otherwise.

Examples:

(define point<%> (interface () get-x get-y))
(define colored-point<%> (interface (point<%>) color))
> (interface-extension? colored-point<%> point<%>)

#t

> (interface-extension? point<%> colored-point<%>)

#f

> (interface-extension? (interface () get-x get-y get-z) point<%>)

#f

procedure

(method-in-interface? sym interface) → boolean?

  sym : symbol?
  interface : interface?
Returns #t if interface (or any of its ancestor interfaces) includes a member with the name sym, #f otherwise.

Examples:

(define i<%> (interface () get-x get-y))
> (method-in-interface? 'get-x i<%>)

#t

> (method-in-interface? 'get-z i<%>)

#f

procedure

(interface->method-names interface) → (listof symbol?)

  interface : interface?
Returns a list of symbols for the method names in interface, including methods inherited from superinterfaces, but not including methods whose names are local (i.e., declared with define-local-member-names).

Examples:

(define i<%> (interface () get-x get-y))
> (interface->method-names i<%>)

'(get-y get-x)

procedure

(object-method-arity-includes? object    
  sym    
  cnt) → boolean?
  object : object?
  sym : symbol?
  cnt : exact-nonnegative-integer?
Returns #t if object has a method named sym that accepts cnt arguments, #f otherwise.

Examples:

(define c%
  (class object%
    (super-new)
    (define/public (m x [y 0])
      (+ x y))))
> (object-method-arity-includes? (new c%) 'm 1)

#t

> (object-method-arity-includes? (new c%) 'm 2)

#t

> (object-method-arity-includes? (new c%) 'm 3)

#f

> (object-method-arity-includes? (new c%) 'n 1)

#f

procedure

(field-names object) → (listof symbol?)

  object : object?
Returns a list of all of the names of the fields bound in object, including fields inherited from superinterfaces, but not including fields whose names are local (i.e., declared with define-local-member-names).

Examples:

> (field-names (new object%))

'()

> (field-names (new (class object% (super-new) (field [x 0] [y 0]))))

'(x y)

procedure

(object-info object) → 
(or/c class? #f) boolean?
  object : any/c
Returns two values, analogous to the return values of struct-info:

  • class: a class or #f; the result is #f if the current inspector does not control any class for which the object is an instance.

  • skipped?: #f if the first result corresponds to the most specific class of object, #t otherwise.

procedure

(class-info class)

 → 
symbol?
exact-nonnegative-integer?
(listof symbol?)
(any/c exact-nonnegative-integer? . -> . any/c)
(any/c exact-nonnegative-integer? any/c . -> . any/c)
(or/c class? #f)
boolean?
  class : class?
Returns seven values, analogous to the return values of struct-type-info:

struct

(struct exn:fail:object exn:fail ()
  #:extra-constructor-name make-exn:fail:object)
Raised for class-related failures, such as attempting to call a method that is not supplied by an object.

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