Re: apple blocks extension

[Chris Lattner <clattner at apple dot com>]

On Sep 24, 2009, at 7:57 AM, Jason Merrill wrote:

> 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.

Can the lambda (containing X) be copied and put onto a queue?  What is  
its type?

-Chris