5.7 Object and Class Contracts

(object-contract member-spec ...)

member-spec   =   (method-id method-contract)     |   (field field-id contract-expr)           method-contract   =   (-> dom ... range)     |   (->* (mandatory-dom ...)      (optional-dom ...)      rest      range)     |   (->d (mandatory-dependent-dom ...)      (optional-dependent-dom ...)      dependent-rest      pre-cond      dep-range)           dom   =   dom-expr     |   keyword dom-expr           range   =   range-expr     |   (values range-expr ...)     |   any           mandatory-dom   =   dom-expr     |   keyword dom-expr           optional-dom   =   dom-expr     |   keyword dom-expr           rest   =       |   #:rest rest-expr           mandatory-dependent-dom   =   [id dom-expr]     |   keyword [id dom-expr]           optional-dependent-dom   =   [id dom-expr]     |   keyword [id dom-expr]           dependent-rest   =       |   #:rest id rest-expr           pre-cond   =       |   #:pre-cond boolean-expr           dep-range   =   any     |   [id range-expr] post-cond     |   (values [id range-expr] ...) post-cond           post-cond   =       |   #:post-cond boolean-expr

Produces a contract for an object.

Each of the contracts for a method has the same semantics as the corresponding function contract, but the syntax of the method contract must be written directly in the body of the object-contract – much like the way that methods in class definitions use the same syntax as regular function definitions, but cannot be arbitrary procedures. The only exception is that ->d contracts implicitly bind this to the object itself.

mixin-contract : contract?

A function contract that recognizes mixins. It guarantees that the input to the function is a class and the result of the function is a subclass of the input.

(make-mixin-contract type ...) → contract?

type : (or/c class? interface?)

Produces a function contract that guarantees the input to the function is a class that implements/subclasses each type, and that the result of the function is a subclass of the input.

(is-a?/c type) → flat-contract?

type : (or/c class? interface?)

Accepts a class or interface and returns a flat contract that recognizes objects that instantiate the class/interface.

(implementation?/c interface) → flat-contract?

interface : interface?

Returns a flat contract that recognizes classes that implement interface.

(subclass?/c class) → flat-contract?

class : class?

Returns a flat-contract that recognizes classes that are subclasses of class.