StackOverflow2013

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copied!<blockquote> <p>In the old days, we were trained to write init methods like this:</p> <p>Foo.h:</p> <pre><code>-(id) initWithInteger: (NSInteger) someNumber; </code></pre> <p>Foo.m:</p> <pre><code>-(id) initWithInteger: (NSInteger) someNumber { if ((self = [super init])) { doSomeStuff; } return self; } </code></pre> <p>But those id casts are now no-nos. So how should these methods now look?</p> </blockquote> <p>Those aren't casts. In that context, that simply syntax declares the return type of the method, as the <code>(NSInteger)</code> part later on declares the type of that argument.</p> <p>The syntax for declaring a method's return type has not changed under ARC. The code you showed would remain exactly the same.</p> <p>Casts are expressions, so a cast of the sort prohibited by ARC can only occur in expression context. For example, if you said:</p> <pre><code>- (id) initWithCFThing:(CFThingRef)thing { if ((self = [super init])) { _thing = (NSThing *)thing; //Casts expression of type CFThingRef to object pointer type NSThing *; this is invalid } return self; } </code></pre> <p>The cast in the assignment expression is invalid, because it casts from a CF object to an Objective-C object pointer (a “retainable object pointer”) with no bridge keyword. The inverse would likewise be invalid:</p> <pre><code>- (CFThingRef) CFThing { return _thing; //Implicitly casts expression of object pointer type NSThing *to type CFThingRef; this is invalid } </code></pre> <p>Same problem in the other direction: The expression given to the <code>return</code> statement casts a retainable object pointer to a CF object type with no bridge keyword.</p> <p>Note where the errors lie. In each case, the error is in an expression: in <code>initWithCFThing:</code>, it's the explicit cast-expression inside the assignment expression; in the accessor <code>CFThing</code>, it's the implicit cast of the expression inside the <code>return</code> statement to the method's return type.</p> <p>In both cases, as in your case, the prototype of the method is completely valid. <code>(CFThingRef)</code> and <code>(id)</code> are still valid, with or without ARC, when you're declaring a return type or argument type for a method. Only as a cast expression is either syntax invalid, because the cast itself is invalid.</p> <p>Adding a bridge keyword satisfies the compiler in a cast expression, because then you're telling it what you want it to do (bridge-crossing casts with no bridge keyword are invalid because the compiler would have to guess what you mean, and it refuses), but would be invalid in a type declaration because that is not ambiguous. The bridge crossing happens at the cast expression (when there is one), not at an argument passage or return.</p>

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