Phobos' std.conv.to-conversion from enum to string doesn't scale beyond hundreds of enumerators

[Per Nordlöw]

On Sunday, 24 June 2018 at 17:23:54 UTC, Steven Schveighoffer 
wrote:
> static if(__traits(compiles, fastEnumToString(val)))
>   return fastEnumToString(val);
> else
>   return slowEnumToString(val); // checks for duplicates
>
> Should eliminate the issues, because it's not going to compile 
> the slow version if the fast version can work.
>
> -Steve

Yes, I thought about that too, but the problem is that 
std.conv.to is used in std.stdio and I don't want to remember to 
always to do

     writeln("Some text:", x.to!string);

instead of

     writeln("Some text:", x);

for some enum instance `x`.

I'm gonna hack up another solution

struct Enum(E)
if (is(E == enum))
{
     @property string toString() @safe pure nothrow @nogc
     {
         // fast implementation
     }
     E _enum;
     alias _enum this;
}

Further, it just struck me that we can generalize my fast 
solution to include enumerations with enumerator aliases that are 
defined directly after its original enumerator by checking with  
a `static if` if the current enumerator value equals the previous 
then we skip it. I'm gonna post the solution here after some 
hacking.