On Tuesday, 25 June 2013 at 10:32:14 UTC, Timothee Cour wrote:

template Test(alias T){
  static if(is(T == TI!TP, alias TI, TP)){
    enum Test=true;
  }
  else{
    enum Test=false;
  }
}

struct A(T){}
void foo(T)(T a){}

void main(){
  static assert(Test!(A!double));
  static assert(!Test!(foo!double)); //why is Test false?
}

This is blocking my pull request to make
fullyQualifiedName/GetTemplateParent/GetTemplateArguments work on
everything: right now it fails on templated functions.

As I have already mentiond in comments to that pull (probably was not clear enough), it is not really a bug, but one of many difficulties when working with function types in generic code.

When you pass a function there, you pass function symbol, not its type. For aggregates those are interchangeable, not so for functions. Most simple example:

    void foo(int x) {}
    pragma( msg, is(foo == function) ); // false
    pragma( msg, is(typeof(foo) == function) ); // true

So you simply can't do any type matching with T when T is function alias.

However, when you take typeof(T), all template information gets lost and you get type of specific instantiation.

Looks like not a bug, but lack of required tool.