On this page:
5.8.1 FFI Types and Constants
_ id
_ Class
_ Protocol
_ SEL
_ BOOL
YES
NO
5.8.2 Syntactic Forms and Procedures
tell
tellv
import-class
import-protocol
define-objc-class
define-objc-mixin
self
super-tell
get-ivar
set-ivar!
selector
objc-is-a?
5.8.3 Raw Runtime Functions
objc_ look Up Class
objc_ get Protocol
sel_ register Name
objc_ allocate Class Pair
objc_ register Class Pair
object_ get Class
class_ add Method
class_ add Ivar
object_ get Instance Variable
object_ set Instance Variable
_ Ivar
objc_ msg Send/ typed
objc_ msg Send Super/ typed
make-objc_ super
_ objc_ super
5.8.4 Legacy Library
objc-unsafe!

5.8 Objective-C FFI

The ffi/unsafe/objc library builds on ffi/unsafe to support interaction with Objective-C.

The library supports Objective-C interaction in two layers. The upper layer provides syntactic forms for sending messages and deriving subclasses. The lower layer is a think wrapper on the Objective-C runtime library functions. Even the upper layer is unsafe and relatively low-level compared to normal Racket libraries, because argument and result types must be declared in terms of FFI C types (see Type Constructors).

5.8.1 FFI Types and Constants

The type of an Objective-C object, an opaque pointer.

The type of an Objective-C class, which is also an _id.

The type of an Objective-C protocol, which is also an _id.

The type of an Objective-C selector, an opaque pointer.

The Objective-C boolean type. Racket values are converted for C in the usual way: #f is false and any other value is true. C values are converted to Racket booleans.

Synonym for #t

Synonym for #f

5.8.2 Syntactic Forms and Procedures

(tell result-type obj-expr method-id)
(tell result-type obj-expr arg ...)
 
result-type = 
  | #:type ctype-expr
     
arg = method-id arg-expr
  | method-id #:type ctype-expr arg-expr
Sends a message to the Objective-C object produced by obj-expr. When a type is omitted for either the result or an argument, the type is assumed to be _id, otherwise it must be specified as an FFI C type (see Type Constructors).

If a single method-id is provided with no arguments, then method-id must not end with :; otherwise, each method-id must end with :.

Examples:

  > (tell NSString alloc)

  #<cpointer:id>

  > (tell (tell NSString alloc)
          initWithUTF8String: #:type _string "Hello")

  #<cpointer:id>

(tellv obj-expr method-id)
(tellv obj-expr arg ...)
Like tell, but with a result type _void.

(import-class class-id ...)
Defines each class-id to the class (a value with FFI type _Class) that is registered with the string form of class-id. The registered class is obtained via objc_lookUpClass.

Example:

  > (import-class NSString)

(import-protocol protocol-id ...)
Defines each protocol-id to the protocol (a value with FFI type _Protocol) that is registered with the string form of protocol-id. The registered class is obtained via objc_getProtocol.

Example:

  > (import-protocol NSCoding)

(define-objc-class class-id superclass-expr
  maybe-mixins
  maybe-protocols
  [field-id ...]
  method)
 
maybe-mixins = 
  | #:mixins (mixin-expr ...)
     
maybe-protocols = 
  | #:protocols (protocol-expr ...)
     
method = (mode result-ctype-expr (method-id) body ...+)
  | (mode result-ctype-expr (arg ...+) body ...+)
     
mode = +
  | -
  | +a
  | -a
     
arg = method-id [ctype-expr arg-id]
Defines class-id as a new, registered Objective-C class (of FFI type _Class). The superclass-expr should produce an Objective-C class or #f for the superclass. An optional #:mixins clause can specify mixins defined with define-objc-mixin. An optional #:protocols clause can specify Objective-C protocols to be implemented by the class.

Each field-id is an instance field that holds a Racket value and that is initialized to #f when the object is allocated. The field-ids can be referenced and set! directly when the method bodys. Outside the object, they can be referenced and set with get-ivar and set-ivar!.

Each method adds or overrides a method to the class (when mode is - or -a) to be called on instances, or it adds a method to the meta-class (when mode is + or +a) to be called on the class itself. All result and argument types must be declared using FFI C types (see Type Constructors). When mode is +a or -a, the method is called in atomic mode (see _cprocedure).

If a method is declared with a single method-id and no arguments, then method-id must not end with :. Otherwise, each method-id must end with :.

If the special method dealloc is declared for mode -, it must not call the superclass method, because a (super-tell dealloc) is added to the end of the method automatically. In addition, before (super-tell dealloc), space for each field-id within the instance is deallocated.

Example:

  > (define-objc-class MyView NSView
      [bm] ; <- one field
      (- _racket (swapBitwmap: [_racket new-bm])
         (begin0 bm (set! bm new-bm)))
      (- _void (drawRect: [_NSRect exposed-rect])
         (super-tell drawRect: exposed-rect)
         (draw-bitmap-region bm exposed-rect))
      (- _void (dealloc)
         (when bm (done-with-bm bm))))

(define-objc-mixin (class-id superclass-id)
  maybe-mixins
  maybe-protocols
  [field-id ...]
  method)
Like define-objc-class, but defines a mixin to be combined with other method definitions through either define-objc-class or define-objc-mixin. The specified field-ids are not added by the mixin, but must be a subset of the field-ids declared for the class to which the methods are added.

When used within the body of a define-objc-class or define-objc-mixin method, refers to the object whose method was called. This form cannot be used outside of a define-objc-class or define-objc-mixin method.

(super-tell result-type method-id)
(super-tell result-type arg ...)
When used within the body of a define-objc-class or define-objc-mixin method, calls a superclass method. The result-type and arg sub-forms have the same syntax as in tell. This form cannot be used outside of a define-objc-class or define-objc-mixin method.

(get-ivar obj-expr field-id)
Extracts the Racket value of a field in a class created with define-objc-class.

(set-ivar! obj-expr field-id value-expr)
Sets the Racket value of a field in a class created with define-objc-class.

(selector method-id)
Returns a selector (of FFI type _SEL) for the string form of method-id.

Example:

  > (tellv button setAction: #:type _SEL (selector terminate:))

(objc-is-a? obj cls)  boolean?
  obj : _id
  cls : _Class
Check whether obj is an instance of the Objective-C class cls.

5.8.3 Raw Runtime Functions

(objc_lookUpClass s)  (or/c _Class #f)
  s : string?
Finds a registered class by name.

(objc_getProtocol s)  (or/c _Protocol #f)
  s : string?
Finds a registered protocol by name.

(sel_registerName s)  _SEL
  s : string?
Interns a selector given its name in string form.

(objc_allocateClassPair cls s extra)  _Class
  cls : _Class
  s : string?
  extra : integer?
Allocates a new Objective-C class.

(objc_registerClassPair cls)  void?
  cls : _Class
Registers an Objective-C class.

(object_getClass obj)  _Class
  obj : _id
Returns the class of an object (or the meta-class of a class).

(class_addMethod cls    
  sel    
  imp    
  type    
  type-encoding)  boolean?
  cls : _Class
  sel : _SEL
  imp : procedure?
  type : ctype?
  type-encoding : string?
Adds a method to a class. The type argument must be a FFI C type (see Type Constructors) that matches both imp and the not Objective-C type string type-encoding.

(class_addIvar cls    
  name    
  size    
  log-alignment    
  type-encoding)  boolean?
  cls : _Class
  name : string?
  size : exact-nonnegative-integer?
  log-alignment : exact-nonnegative-integer?
  type-encoding : string?
Adds an instance variable to an Objective-C class.

(object_getInstanceVariable obj name)  
_Ivar any/c
  obj : _id
  name : string?
Gets the value of an instance variable whose type is _pointer.

(object_setInstanceVariable obj name val)  _Ivar
  obj : _id
  name : string?
  val : any/c
Sets the value of an instance variable whose type is _pointer.

The type of an Objective-C instance variable, an opaque pointer.

((objc_msgSend/typed types) obj sel arg)  any/c
  types : (vector/c result-ctype arg-ctype ...)
  obj : _id
  sel : _SEL
  arg : any/c
Calls the Objective-C method on _id named by sel. The types vector must contain one more than the number of supplied args; the first FFI C type in type is used as the result type.

((objc_msgSendSuper/typed types)    
  super    
  sel    
  arg)  any/c
  types : (vector/c result-ctype arg-ctype ...)
  super : _objc_super
  sel : _SEL
  arg : any/c
Like objc_msgSend/typed, but for a super call.

(make-objc_super id super)  _objc_super
  id : _id
  super : _Class
_objc_super : ctype?
Constructor and FFI C type use for super calls.

5.8.4 Legacy Library

The ffi/objc library is a deprecated entry point to ffi/unsafe/objc. It exports only safe operations directly, and unsafe operations are imported using objc-unsafe!.

Analogous to (unsafe!), makes unsafe bindings of ffi/unsafe/objc available in the importing module.