Shorten My Objective-C Code Using Blocks

Question

This is from a category that I'm using to modify UIView. The code works, but in the first method (setFrameHeight) I'm using a block and in the second method (setFrameWidth) I'm not. Is there any way to use blocks more efficiently in this example?

typedef CGRect (^modifyFrameBlock)(CGRect);

- (void) modifyFrame:(modifyFrameBlock) block {
    self.frame = block(self.frame);
}

- (void) setFrameWidth:(CGFloat)newWidth {
    modifyFrameBlock b = ^CGRect (CGRect frame) { 
        frame.size.width = newWidth;
        return frame; 
    };      
    [self modifyFrame:b];
}

- (void) setFrameHeight:(CGFloat)newHeight {
    CGRect f = self.frame;
    f.size.height = newHeight;
    self.frame = f;
}

The answer may be that blocks are not appropriate for such short methods, or something. The syntax sure seems funky.

Answer 1

The only thing you gain is not declaring the local variable for the new rect, in exchange you need to define a block. That is not a good deal, especially as it distracts from what you are doing.

Note that your block-usage could be shortened a bit:

[self modifyFrame:^(CGRect frame) {
    frame.size.width = newWidth;
    return frame; 
}];

Or even:

[self modifyFrame:^(CGRect* frame) {
    frame->size.width = newWidth;
}];

With modifyFrame: being:

CGRect frame;
block(&frame);
self.frame = frame;

But i'd still limit such approaches to more complex methods that only require minor parts of the code to be different.

Answer 2

This particular pattern is useful in other situations (generally where extensibility is needed at runtime) and is frequently seen in C with function pointers in place of blocks (e.g. qsort() and bsearch().) For just updating a field, however, the usual way is to just call from the simpler method to the more complex one:

- (void)setDisplaysUserInterface: (BOOL)flag {
    [self setDisplaysUserInterface: flag animated: YES];
}


- (void)setDisplaysUserInterface: (BOOL)flag animated: (BOOL)animated {
    [self setDisplaysUserInterface: flag animated: animated hideAfterDelay: NAN];
}

- (void)setDisplaysUserInterface: (BOOL)flag animated: (BOOL)animated hideAfterDelay: (NSTimeInterval)hideDelay {
    // and so forth
}