How to write lambda methods in Objective-C?

How to write lambda methods in Objective-C?

How to write lambda methods in Objective-C ?

objective-c protocol defined in its own .h file?


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The concept of a lambda in Objective-C is now encapsulated with the idea of Blocks which are the equivalent of pass-by-reference functions.

Objective-c static instance
Of course, arguably one had that already in C with the idea of function pointers; blocks are just a way of also capturing local state (i.e.

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can be closures).

Why are instance variables defined in the header file in Objective-C
In fact, blocks can also be used in other C languages as well (on Mac) - there's a proposal to make them part of the standard C syntax..
What class of Objective-C variable is this?
Here's an example of defining a lambda to multiply two numbers together:.
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int (^mult)(int, int) = ^(int a, int b) { return a*b }; 
The first part declares a variable, of type ^int(int,int) and then assigns it to the lambda expression (aka block) which returns the multiple of its two arguments.

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You can then pass that fn around, define it in other places etc; you can even use it in other functions.. Here's an example of defining a function, which when invoked, returns another function:.
multiplyBy = ^(int a) { return ^(int b) { return b*a; }; }; triple = multiplyBy(3); 
Note that you can intermix blocks with object types (usually using id as the object type) and many of the new Objective-C object data structures have some kind of block-level operation.

GCD also uses blocks in order to pass in arbitrary events; however, note that GCD can also be used with function pointers as well..


OS X 10.6 introduced blocks.

See AlBlue's answer for examples.. If you're not using Snow Leopard, you can get something close to function composition using various other features.. Example using C function pointers:.
void sayHello() {     NSLog(@"Hello!"); }  void doSomethingTwice(void (*something)(void)) {     something();     something(); }  int main(void) {     doSomethingTwice(sayHello);     return 0; } 
Example using the command pattern:.
@protocol Command <NSObject> - (void) doSomething; @end  @interface SayHello : NSObject <Command> { } @end  @implementation SayHello - (void) doSomething {     NSLog(@"Hello!");     } @end  void doSomethingTwice(id<Command> command) {     [command doSomething];     [command doSomething]; }  int main(void) {     SayHello* sayHello = [[SayHello alloc] init];     doSomethingTwice(sayHello);     [sayHello release];     return 0; } 
Example using a selector:.
@interface SaySomething : NSObject { } - (void) sayHello; @end  @implementation SaySomething - (void) sayHello {     NSLog(@"Hello!");     } @end  void doSomethingTwice(id<NSObject> obj, SEL selector) {     [obj performSelector:selector];     [obj performSelector:selector]; }  int main(void) {     SaySomething* saySomething = [[SaySomething alloc] init];     doSomethingTwice(saySomething, @selector(sayHello));     [saySomething release];     return 0; } 


I heard André Pang at NSConference talking about how blocks were going to be introduced with the next version of Objective-C.. This should allow functional programming.. Edit: Since Snow Leopard has been released, this is indeed the case.

Objective-C now has Blocks..

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