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List Comprehension
NSArray *a = @[@"Hello", @"Will This work?", @"can it work?", @"Yes!"];
// sure, this works...
NSMutableArray *b = [NSMutableArray arrayWithCapacity:[a count]];
[a enumerateObjectsUsingBlock: ^(id obj, NSUInteger idx, BOOL *stop) {
[b insertObject: [obj uppercaseString] atIndex: idx];
// but it assumes that the enumeration is always increasing
// you can't go through the array backwards (or concurrently)
[a enumerateObjectsWithOptions:NSEnumerationReverse usingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
[b insertObject:[obj uppercaseString] atIndex:idx]; // crash!
// why not just a simple for loop? It's also the fastest...
NSMutableArray * b = [NSMutableArray arrayWithCapacity:[a count]];
for (id item in a) {
[b addObject:[item uppercaseString]];
// or even edit the array in-place?*
NSMutableArray *b = [NSMutableArray arrayWithArray:a];
for (__strong id item in b) { // __strong is for ARC
item = [item uppercaseString];
// * only works for NSStrings, not NSNumbers. No idea why!
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