Converting a type to a char

[Paul Backus]

On Friday, 25 January 2019 at 15:53:10 UTC, Thomas Gregory wrote:
> I would like to check that a char (unknown at compile time) 
> matches a particular type but I would like to do so without if 
> statements or a hash map as I would like it to be as fast as 
> possible.
>
> Ideally I would choose something like this:
>
> enum typeIndex{
> byte = 0,
> ubyte,
> short,
> ushort,
> int,
> uint
> }
>
> char[6] typechars="cCsSiI";
>
> bool check(T)(char c){
>    return typechars[typeIndex(typeof(T))]==c;
> }
>
> Though I know this is implementation is not remotely correct D.

You can do this with AliasSeq and staticIndexOf:

import std.meta;

alias Types = AliasSeq!(byte, ubyte, short, ushort, int, uint);
enum typeIndex(T) = staticIndexOf!(T, Types);
char[6] typechars="cCsSiI";

bool check(T)(char c) {
     return typechars[typeIndex!T] == c;
}

Runnable version: https://run.dlang.io/is/Tps38K