5.8 Objective-C FFI

► |  | FFI: Racket Foreign Interface

1 | Overview
2 | Loading Foreign Libraries
3 | C Types
4 | Pointer Functions
5 | Derived Utilities
6 | Miscellaneous Support
7 | Unexported Primitive Functions
| Index

▼ | 5 | Derived Utilities

5.1 | Safe Homogenous Vectors
5.2 | Safe C Vectors
5.3 | Tagged C Pointer Types
5.4 | Defining Bindings
5.5 | Allocation and Finalization
5.6 | Atomic Execution
5.7 | Speculatively Atomic Execution
5.8 | Objective-C FFI

► | 5.8 | Objective-C FFI

5.8.1 | FFI Types and Constants
5.8.2 | Syntactic Forms and Procedures
5.8.3 | Raw Runtime Functions
5.8.4 | Legacy Library

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!

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#### 5.8`` Objective-C FFI

( require ffi/unsafe/objc)

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

_id : ctype?

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

_Class : ctype?

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

_Protocol : ctype?

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

_SEL : ctype?

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

_BOOL : ctype?

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.

YES : boolean?

Synonym for #t

NO : boolean?

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.

self

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.

_Ivar : ctype?

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

( require ffi/objc)

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!.

( objc-unsafe!)

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