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copied!<h2>List of Block Declaration Syntaxes</h2> <p>Throughout, let</p> <ul> <li><code>return_type</code> be the type of object/primitive/etc. you'd like to return (commonly <code>void</code>)</li> <li><code>blockName</code> be the variable name of the block you're creating</li> <li><code>var_type</code> be the type object/primitive/etc. you'd like to pass as an argument (leave blank for no parameters)</li> <li><code>varName</code> be the variable name of the given parameter</li> </ul> <p>And remember that you can create as many parameters as you'd like.</p> <h3>Blocks as Variables</h3> <p>Possibly the most common for of declaration.</p> <pre><code>return_type (^blockName)(var_type) = ^return_type (var_type varName) { // ... }; </code></pre> <h3>Blocks as Properties</h3> <p>Much like declaring blocks as variables, however subtly different.</p> <pre><code>@property (copy) return_type (^blockName) (var_type); </code></pre> <h3>Blocks as Parameters</h3> <p>Note that this is distinct from "Blocks as Arguments"; in this instance, you're declaring a method that wants a block argument.</p> <pre><code>- (void)yourMethod:(return_type (^)(var_type))blockName; </code></pre> <h3>Blocks as Arguments</h3> <p>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.</p> <pre><code>[someObject doSomethingWithBlock: ^return_type (var_type varName) { //... }]; </code></pre> <h3>Anonymous Block</h3> <p>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.</p> <pre><code>^return_type (var_type varName) { //... }; </code></pre> <h3><code>typedef</code> Block</h3> <p>This allows you to set up a short name that can be referenced just like any other class name during the declaration of blocks.</p> <pre><code>typedef return_type (^blockName)(var_type); </code></pre> <p>To then later use <code>blockName</code> instead of the standard block declaration syntax, simply substitute.</p> <h3>Inline Block</h3> <p>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.</p> <pre><code>^return_type (var_type varName) { //... }(var); </code></pre> <p>Inline blocks are primarily useful for scope offsetting, and are roughly equivalent to simple brace-delimited chunks of code.</p> <pre><code>{ //... } </code></pre> <h3>Recursive Blocks</h3> <p>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.</p> <pre><code>__block return_type (^blockName)(var_type) = [^return_type (var_type varName) { if (returnCondition) { blockName = nil; return; } // ... } copy]; blockName(varValue); </code></pre> <h3>Returning Blocks</h3> <p>A method can return a block,</p> <pre><code>- (return_type(^)(var_type))methodName { // ... } </code></pre> <p>as can a function, if a bit strangely.</p> <pre><code>return_type (^FunctionName())(var_type) { // ... } </code></pre> <h2>Addendums</h2> <p>If I've missed anything, please let me know in comments, and I'll research/add them.</p> <h2>Oh, and in Swift...</h2> <pre><code>blockName = (varName: var_type) -> (return_type) </code></pre> <p>It's almost like it's a language feature.</p>

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