Consider http://dpaste.dzfl.pl/fork/ae75176d7d3f.

It's a bit roundabout but in brief it instantiates a template with a nested function. The nested function, in turn, uses a parameter in its environment. By the canon, that function needs to create a closure with dynamically-allocated environment.

To my surprise, however, the generated code uses no closure (disassembly at http://goo.gl/ti23W0) yet works correctly.

How come? Can anyone explain to me where x (used by the nested function) is stored?


Thanks,

Andrei

P.S. I'd like to thank Iain and Vladimir for making it so easy and pleasing to inspect and share code snippets with dpaste and asm.dlang.org.

On 6/2/2015 11:05 PM, Andrei Alexandrescu wrote:
> Consider http://dpaste.dzfl.pl/fork/ae75176d7d3f.
>
> It's a bit roundabout but in brief it instantiates a template with a nested
> function. The nested function, in turn, uses a parameter in its environment. By
> the canon, that function needs to create a closure with dynamically-allocated
> environment.
>
> To my surprise, however, the generated code uses no closure (disassembly at
> http://goo.gl/ti23W0) yet works correctly.
>
> How come? Can anyone explain to me where x (used by the nested function) is stored?

It doesn't avoid creating a closure. The dpaste compiler is not showing the call to __d_allocmemory because it is incorrectly resolving it to another symbol.

(A closure can be detected by the presence of a call to __d_allocmemory.)