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How to Memorize Block Syntax

Since block syntax came out alongside iOS 4, I’ve struggled to memorize it. Sure, blocks without return types or parameters = ^{ return @”super easy to recall”;}, but once you factor in arguments and want to accept a block argument in a method, thingsBecome:(CGFloat (^)(NSInteger way, id more, CGRect complex))dontYaThink?

It’s no wonder that Fucking Block Syntax has become one of my most beloved websites.

But if you’re not the Rain Man and, like me, have trouble remembering the syntax accurately, there’s hope! I have a full-proof way to memorize it.

The Two Basic Forms

There are two basic forms to memorize. The first is when your block has a name, and the second when your block is a value (anonymous):

  1. NSInteger (^myBlockName)(CGFloat param1)
  2. ^NSInteger(CGFloat param1)

Take a minute to look at these two forms. The first form is as normal and expected as could be. REMEMBER, put the block name in parenthesis. If you do that, it’s easy pickings. The ^ is like a * if the function was a pointer. Just remember those parenthesis. Visualize how the parenthesis cuddle the name of the block. Think: Cuddle The Name.

The second form is ridiculous. Backwards almost. Since there is no name associated with the block, the return type flips to the other side of the carat. No cuddling needed, either. Clearly, tho, dropping the name means we can compact the syntax. I like to remember the phrase, Flip No Cuddle. To me, we flip the side of the carat the return type is on and lose the parentheses.

Apply It Everywhere

With these two concepts in mind, the named block and the anonymous block, let’s see them all applied. Read the following sample code and identify each one, repeating the above phrases as you see each one. Recognize if the block is named or not, then say either Cuddle The Name or Flip No Cuddle:

// pass block to method
[self makeNumberFromString:^NSNumber *(NSString *str) { ... }];

// define block locally
NSNumber * (^local)(NSString *str) = nil;

// property
@property (copy, nonatomic) NSNumber * (^myProp)(NSString *str);

// the defined method
- (void)makeNumberFromString:(NSNumber * (^)(NSString *str))named {

How did you do? Your answers should have been Flip No Cuddle, Cuddle The Name, Cuddle The Name, and WHAT THE F*** ARE YOU KIDDING ME? Yep, sorry, method parameters bend the Cuddle The Name mold a bit by flipping the method name to the outside. However, this too is easy to remember because the carat remains and, hey, ALL method parameters put their name on the outside. Right?

- (BOOL)textFieldShouldReturn:(UITextField *)textField { ... }

So, just put the whole expression in parens and the parameter name on the outside like you always do.

Typedefs? Cuddle The Name!

I’m not a huge fan of typedefs for blocks, but you’ll see them used often and you should recognize easily that defining them is Cuddle The Name:

typedef BOOL (^IsItSafeType)(NSInteger);

With it defined, assigning to it is what pattern? RIGHT! It’s Flip No Cuddle because you assign an anonymous value to the variable!

IsItSafeType alwaysSafe = ^BOOL(NSInteger x) { return YES; };

OK, Let’s Summarize!

Alright, so we have our two basic forms:

  • NSInteger (^myBlockName)(CGFloat param1) <-- Cuddle The Name for named blocks
  • ^NSInteger(CGFloat param1) <-- Flip No Cuddle for anonymous blocks

The one exception is with Cuddle The Name for method parameters where we cuddle the whole thing and pull the parameter name outside:

  • ((NSInteger (^)(CGFloat param1))outsideName <-- Cuddle The Name wants to be like other parameters!

But as you can see, since it’s a named block, using Cuddle The Name is perfectly consistent. Then, defining typedefs, we still have a named block and so we use Cuddle The Name there, too! And assigning to the typedef? Yep. Flip No Cuddle.

Simple! Hopefully, this helps us memorize this very strange syntax. :-)

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John Blanco

John Blanco is a freelance iOS developer in Denver, CO. He's been developing mobile apps for 12 years, starting during the medieval days of Java ME, making him the ultimate hipster mobile engineer. Follow him on Twitter!

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