6.11 Object, Class, and Interface Utilities

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6.11 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 whether a and b were returned from the same call to new or not. If the two objects have fields, this procedure determines whether mutating a field of one would change that field in the other.

This procedure is similar in spirit to eq? but also works properly with contracts (and has a stronger guarantee).

Examples:

(define obj-1 (new object%))

(define obj-2 (new object%))

> (define/contract obj-3 (object/c) obj-1)
> (object=? obj-1 obj-1)
#t
> (object=? obj-1 obj-2)
#f
> (object=? obj-1 obj-3)
#t
> (eq? obj-1 obj-1)
#t
> (eq? obj-1 obj-2)
#f
> (eq? obj-1 obj-3)
#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:106:0 ...)

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 cls) → boolean?
v : any/c
cls : class?

Returns #t if v is a class derived from (or equal to) cls, #f otherwise.

Examples:

> (subclass? (class object% (super-new)) object%)
#t
> (subclass? object% (class object% (super-new)))
#f
> (subclass? object% object%)
#t

procedure
(implementation? v intf) → boolean?
v : any/c
intf : interface?

Returns #t if v is a class that implements intf, #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 intf) → boolean?
v : any/c
intf : interface?

Returns #t if v is an interface that extends intf, #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 intf) → boolean?
sym : symbol?
intf : interface?

Returns #t if intf (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 intf) → (listof symbol?)
intf : interface?

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

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-name).

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 : object?

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:

name: the class’s name as a symbol;
field-cnt: the number of fields (public and private) defined by the class;
field-name-list: a list of symbols corresponding to the class’s public fields; this list can be larger than field-cnt because it includes inherited fields;
field-accessor: an accessor procedure for obtaining field values in instances of the class; the accessor takes an instance and a field index between 0 (inclusive) and field-cnt (exclusive);
field-mutator: a mutator procedure for modifying field values in instances of the class; the mutator takes an instance, a field index between 0 (inclusive) and field-cnt (exclusive), and a new field value;
super-class: a class for the most specific ancestor of the given class that is controlled by the current inspector, or #f if no ancestor is controlled by the current inspector;
skipped?: #f if the sixth result is the most specific ancestor class, #t otherwise.

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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1	Language Model
2	Notation for Documentation
3	Syntactic Forms
4	Datatypes
5	Structures
6	Classes and Objects
7	Units
8	Contracts
9	Pattern Matching
10	Control Flow
11	Concurrency and Parallelism
12	Macros
13	Input and Output
14	Reflection and Security
15	Operating System
16	Memory Management
17	Unsafe Operations
18	Running Racket
	Bibliography
	Index

6.1	Creating Interfaces
6.2	Creating Classes
6.3	Creating Objects
6.4	Field and Method Access
6.5	Mixins
6.6	Traits
6.7	Object and Class Contracts
6.8	Object Equality and Hashing
6.9	Object Serialization
6.10	Object Printing
6.11	Object, Class, and Interface Utilities
6.12	Surrogates