Nothrow std.conv.to with explicit default value

[Per Nordlöw]

On Wednesday, 20 June 2018 at 09:37:00 UTC, Per Nordlöw wrote:
> AFAICT, string-to-enum-conversion must include a switch 
> containing a static foreach over all the enumerators, right?

My suggestion for nothrow @nogc string-to-enum conversion with 
default value


T toDefaulted(T)(scope const(char)[] value,
                  T defaultValue) @safe pure nothrow @nogc
if (is(T == enum))
{
     switch (value)
     {
         static foreach (index, member; __traits(allMembers, T))
         {
         case member:
             return cast(T)(index);
         }
     default:
         return defaultValue;
     }
}

@safe pure nothrow /*TODO @nogc*/ unittest
{
     enum E { unknown, x, y, z }
     assert("x".toDefaulted!(E)(E.init) == E.x);
     assert("_".toDefaulted!(E)(E.init) == E.unknown);
}