trusted purity?

[Henning Pohl]

I've been working on a pull request and came up with something 
like this:

private void initialize(A...)(auto ref A args)
{
     auto m = cast(void* function(size_t size) pure)&malloc;
     _store = cast(Impl*) enforce(m(Impl.sizeof));
     auto r = cast(void function(in void* p, size_t sz) nothrow 
pure)&GC.addRange;
     static if (hasIndirections!T)
         r(&_store._payload, T.sizeof);
     emplace(&_store._payload, args);
     _store._count = 1;
}

The purity of "emplace" depends on the purity of the ctor called. 
I'm not sure how to fix that.