On Jul 19, 2011, at 3:42 PM, Kyle Sluder wrote:
> Hi all,
>
> The section "Patterns to Avoid" of the Blocks Programming Topics Guide
> warns against the following pattern:
> http://developer.apple.com/library/ios/#DOCUMENTATION/Cocoa/Conceptual/Blocks/Articles/bxUsing.html#//apple_ref/doc/uid/TP40007502-CH5-SW2
>
>
> void dontDoThisEither() {
> void (^block)(void);
>
> int i = random():
> if (i > 1000) {
> block = ^{ printf("got i at: %d\n", i); };
> // WRONG: The block literal scope is the "then" clause
> }
> // ...
> }
>
>
> But I was curious about whether the following was legal, since the
> lack of curly braces around the if statement's then-clause means no
> new scope is introduced:
>
> void howAboutThis() {
> void (^block)(void) = nil;
>
> if (someCondition)
> block = ^{ printf("Hello\n"); }
>
> // ...
>
> [foo doSomethingWithBlock:block];
> }
>
> My understanding is that the compiler should keep the block live on
> the stack until the very end of the function, whereas in the
> documented example the compiler is free to reuse the block's slot on
> the stack as soon as control has exited the if block's bracketed
> then-clause.
No such luck. An `if` clause with no curly braces still defines a scope. Your block object may still die too early.
ARC fixes this. It will copy the block unless the optimizer determines that it is safe not to.
--
Greg Parker email@hidden Runtime Wrangler
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