List of Block Declaration Syntaxes

gistfile1.md

Blocks as Variables

Possibly the most common for of declaration.

return_type (^blockName)(var_type) = ^return_type (var_type varName)
{
    // ...
};

Blocks as Properties

Much like declaring blocks as variables, however subtly different.

@property (copy) return_type (^blockName) (var_type);

Blocks as Parameters

Note that this is distinct from "Blocks as Arguments"; in this instance, you're declaring a method that wants a block argument.

- (void)yourMethod:(return_type (^)(var_type))blockName;

Blocks as Arguments

Note that this is distinct from "Blocks as Parameters"; in this instance, you're calling a method that wants a block argument with an anonymous block. If you have already declared a block variable, it is sufficient to pass the variable name as the argument.

[someObject doSomethingWithBlock: ^return_type (var_type varName)
{
    //...
}];

Anonymous Block

This is functionally an anonymous block, however the syntax for assigning blocks to variables is simply to set the variable equal to an anonymous block.

^return_type (var_type varName)
{
    //...
};

typedef Block

This allows you to set up a short name that can be referenced just like any other class name during the declaration of blocks.

typedef return_type (^blockName)(var_type);

To then later use blockName instead of the standard block declaration syntax, simply substitute.

Inline Block

This is arguably a less useful utilization of blocks, but may have its place nonetheless. An inline block is an anonymous block called immediately after instantiation.

^return_type (var_type varName)
{
    //...
}(var);

Inline blocks are primarily useful for scope offsetting, and are roughly equivalent to simple brace-delimited chunks of code.

{
   //...
}

Recursive Blocks

This allows you to call a block from itself, creating a loop that can be used during callbacks and GCD calls. This instantiation method is free of retain cycles in ARC.

__block return_type (^blockName)(var_type) = [^return_type (var_type varName)
{
    if (returnCondition)
    {
        blockName = nil;
        return;
    }

    // ...
} copy];
blockName(varValue);

Returning Blocks

A method can return a block,

- (return_type(^)(var_type))methodName
{
    // ...
}

as can a function, if a bit strangely.

return_type (^FunctionName())(var_type)
{
    // ...
}

http://stackoverflow.com/questions/9201514/block-declaration-syntax-list#answer-9201774