apple blocks extension

[Jason Merrill]

On 09/15/2009 12:35 PM, Chris Lattner wrote:
> The second major feature of Blocks vs c++ lambdas is that they can be
> "copied onto the heap". This allows things like "Grand Central Dispatch"
> to work: you can write code that executes blocks asynchronously or on
> other threads/work queues (after the function containing the block has
> returned). A simple example is:
>
> void print_on_different_thread(int X) {
>   run_asynch(^{
>     printf("Hi %d\n", X);
>   });
> }
>
> With lambdas, the closure would be go out of scope when
> print_on_different_thread returns, but blocks allows "run_asynch" to
> extend the lifetime of the block.

The lambda equivalent would be

void print_on_different_thread(int X) {
   run_asynch([=]{
     printf("Hi %d\n", X);
   });
}

since X is captured by copy, run_asynch can do whatever it wants with 
the closure and not worry about the original X going away.

The only difference between blocks and lambdas here seems to be where 
you decide to copy the locals off the stack.

Jason