Can you store functions in an array in Objective C?

Question

I want to make an array of functions so that I could randomize the order in which these arrays happen. Could I do something like:

NSMutableArray *MyArray = [NSMutableArray arrayWithObjects: function1, function2, function3, nil];

So that if I could do something like this;

RandomNum = arc4random() %([MyArray count]);
MyArray[RandomNum];

Thus Randomizing the order in which these functions are called in? How do I store the functions in this array?

Please specify the language you're using. Also add it to your post's tags. — Tomáš Zato, Feb 09 '14 at 14:19
And do you mean c functions, blocks, or selectors for methods? — Max, Feb 09 '14 at 14:23
Have a look at Objective-C blocks: http://stackoverflow.com/questions/7997666/storing-blocks-in-an-array and NSInvocation: http://stackoverflow.com/questions/313400/nsinvocation-for-dummies — Atomix, Feb 09 '14 at 14:29

score 4 · Accepted Answer · answered Feb 09 '14 at 14:30

As for ObjC blocks you can just store them in an NSArray directly. Plain C functions have to be wrapped into an NSValue:

NSArray *functions = @[[NSValue valueWithPointer:function1], [NSValue valueWithPointer:function2]];

Then you can call them as follow, just make sure you cast it to correct signature:

((void (*)(int))[functions[RandomNum] pointerValue])(10);

Daij-Djan · Answer 2 · 2014-02-09T14:54:51.217

There ways come to mind

you can store blocks in an array
but you can also method invocations there if you want to call methods and not blocks (you would do the latter via NSInvocation)
For C functions, wrap them in an NSValue to store them and call em later

sample 1 -- blocks

    NSMutableArray *array = [NSMutableArray array];
    [array addObject:^{ /* block */ }];

sample 2 -- invocation

    NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:[object methodSignatureForSelector:selector]];
    invocation.target = object;
    invocation.selector = selector;
    [array addObject:invocation];

sample 3 -- C-Function

    [NSValue valueWithPointer:function1]

score 1 · Answer 3 · edited May 23 '17 at 12:14

Blocks will be the best approach, but I you are not familiar with blocks or from ant other reason you can use: NSSelectorFromString & NSStringFromSelector.

EDITED

Store the methods in array with NSStringFromSelector
You can then shuffle the array as described here : Shuffling array
call the functions using NSSelectorFromString.

For Example

NSArray * functions = @[NSStringFromSelector(selector1),NSStringFromSelector(selector2),
NSStringFromSelector(selector3),NSStringFromSelector(selector4)];

//shuffle the array (see link)
 [functions shuffle];

 [arr enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
       [self performSelector:NSSelectorFromString(functions[idx]) withObject:nil];
 }];

(The code was written on the fly, please check it out).

score 1 · Answer 4 · answered Feb 09 '14 at 14:41

Store a pointer to a function in an array and call the function:

#import <Foundation/Foundation.h>

static void hello() {
    NSLog(@"hey\n");
}

int main(int argc, char *argv[]) {
    @autoreleasepool {
        NSPointerArray *array = [NSPointerArray pointerArrayWithOptions:NSPointerFunctionsOpaqueMemory];
        [array addPointer: &hello];
        void* ptr = [array pointerAtIndex:0];
        ((void (*)(void)) ptr)(); // prints hey
    }
}

Can you store functions in an array in Objective C?

4 Answers4