ImplicitConversionTargets opposite

[Baz via Digitalmars-d-learn]

On Thursday, 21 May 2015 at 21:49:55 UTC, Freddy wrote:
> std.traits has ImplicitConversionTargets.
> Is there any template that returns the types that can implicty 
> convert to T?

You can write something like this:

---
import std.stdio;
import std.traits;
import std.typetuple;

void main(string[] args)
{

     template PossibleType(From)
     {
         private alias All = 
TypeTuple!(byte,ubyte,short,ushort,int,uint);
         private alias Convertible(To) = 
isImplicitlyConvertible!(From,To);
         public alias PossibleType = Filter!(Convertible, All);
     }

     writeln((PossibleType!int).stringof);
     writeln((PossibleType!short).stringof);
}
---

which outputs:

---
(int, uint)
(short, ushort, int, uint)
---

The idea is to reduce the list of all the possible types. It's 
easy because the high-order functional functions are implemented 
for the type list.

`All` could be a template parameter, and more filled, but to keep 
the example simple here it's not.