pureity of closures

[via Digitalmars-d]

On Monday, 30 March 2015 at 13:18:44 UTC, Dicebot wrote:
> On Sunday, 29 March 2015 at 12:29:13 UTC, Stefan Koch wrote:
>> On Friday, 27 March 2015 at 17:47:26 UTC, H. S. Teoh wrote:
>>> What I'm more concerned about is whether the current compiler
>>> implementation may accidentally allow leakage of the pure 
>>> function's
>>> internal context, which would break purity.
>>>
>>>
>>> T
>> please explain your reasoning with a bit of example code.
>> I am not sure if I get where/when impurity would be introduced.
>
> void delegate() metafoo() pure
> {
>     int x;
>     return () { x = 42; }; // now stack frame of pure function
>                            // is available externally
>                            // no idea what may happen
> }

Hmmm... Where's the (conceptual) difference to this:

struct S {
     int x;
     void foo() pure {
         x = 42;
     }
}

S* metafoo() pure {
     auto s = new S;
     return s;
}

Why should your example be impure?