__Symbol an alternative to recursive templates for type-introsecption

[Stefan Koch via Digitalmars-d]

Hi Guys,

You might remember my critique regarding the 
fullyQulifiedName-template in phobos.
Basically it is dramatically slowed down by the cost of template 
instanciation.
I tried to remedy the situation by using by introducing another 
__trait.
While this succeeded in reducing the compile-time drastically,
It was deemed a bad precedent to replace library functionality 
with compiler intrinsics.

If we were to introduce a new that could hold a symbol.
(akin to AliasSeq!(...)[0]), only much less expensive :))
Then we could replace the fqn template with this :

template fqn(alias T)
{
  string fqn = ()
  {
    string result = (cast(__Symbol)T).name;
    __Symbol t = cast(__Symbol)T;
    __Symbol p = t.parent;
    while(p)
    {
      result = p.name ~ "." ~ result;
      t = p;
    }
    return result
  }();
}

As you can see there is only CTFE and no recursive template 
instanciation.
Thereby the currently worst factor would be removed.

The pseudo-type __Symbol is only valid at CT.

It can only be obtained by either a TemplateAliasParameter or 
from a member-variable of another __Symbol.

So far it can be visualized as
struct __Symbol
{
  string name;
  __Symbol parent;
  /* MaybeLater:
  __SymbolType type;
  __Symbol[] members;
  ....
 */
}