Blocks vs Functions in Objective-C

Question

What is the difference between blocks and functions in Objective-C?

Answer 1

The block is an "anonymous function", which you assign to a variable and/or pass on as parameter. Since the function has no name, you can only use it if you have a direct reference.

Example taken from Apple documentation: (https://developer.apple.com/library/ios/documentation/cocoa/Conceptual/Blocks/Articles/bxGettingStarted.html#//apple_ref/doc/uid/TP40007502-CH7-SW1)

int (^myBlock)(int) = ^(int num) {
    return num * multiplier;
};

The block is similar to the Ruby code block, the Javascript Function(), it is also similar to the closure present in many languages, but with limitations.

The block is interesting when you have to callback Cocoa. Often this callback is short, and it is bureaucratic to create another method or function just to pass it on.

Quite common situation in animations. Example taken from https://stackoverflow.com/questions/12292044/putting-a-fade-in-fadeout-effect-on-objective-c

 [UIView animateWithDuration:0.5f animations:^{
        // fade out effect
        _self.myView.alpha = 0.0f;
    } completion:^(BOOL success){
        [UIView animateWithDuration:0.5f animations:^{
            // fade in effect
            _self.myView.alpha = 1.0f;
        } completion:^(BOOL success){
            // recursively fire a new animation
            if (_self.fadeInOutBlock)
                _self.fadeInOutBlock();
        }];
    }];