Escaped scoped

[Steven Schveighoffer]

On Mon, 04 Jan 2010 05:52:19 -0500, bearophile <bearophileHUGS at lycos.com>  
wrote:

> If I compile the following code with DMD with and without the scope  
> annotation I can see that both versions compile and the version with  
> scope deletes the object. Is the compiler acting correctly here? I'd  
> like the compiler to refuse to compile this code when the scope  
> attribute is present (this is a reduced example from a bug I've just  
> removed from a program of mine):
>
> class Foo {}
> class Bar {
>     Foo x;
>     void spam() {
>         scope Foo temp = new Foo();
>         this.x = temp;
>     }
> }
> void main() {}

Scope is not a type constructor, so once the compiler passes the line

scope Foo temp = new Foo();

the compiler sees temp as type Foo, not scope Foo.  So it is ignorant on  
the next line to know to stop you from doing something foolish.

When using scope, it is on you to ensure that it doesn't escape.

I think the compiler cheats a little bit on delegates, but it has severe  
limitations that I think make using delegates without accidentally  
allocating closures difficult.

-Steve