Using Objective-C blocks for encapsulation while preparing a local variable.

gistfile1.m

NSArray *things = ^{
    NSMutableArray *tmpArray = [NSMutableArray arrayWithCapacity:numThings];
    for (int i = 0; i < numThings; i++)
    {
        [tmpArray addObject: ... ];
    }
    return [tmpArray copy];
}();


// Using a category method:
NSArray *things = [NSArray ap_arrayViaMutable:^(NSMutableArray *a) {
    [a addObject: ... ];
    ...
}];