TypeFunction example: ImplictConvTargets

[Adam D. Ruppe]

On Monday, 5 October 2020 at 11:44:34 UTC, Stefan Koch wrote:
> I leave it up to you to decide which version is more 
> understandable and extendable (should we ever get another basic 
> type :))

Also trivially easy with mixins. Normally I don't suggest doing 
things this way but for basic types mixin is guaranteed to work.

```

enum basic_types = ["bool", "ubyte", "char", "byte", "ushort", 
"wchar", "short", "uint", "dchar", "int", "ulong", "long"];

// to not import stdlib
alias AliasSeq(T...) = T;
string join(string[] s, string j) {
         string a;
         foreach(i; s)
                 a ~= i ~ j;
         return a;
}

template basicTypeConvTargets(T) {
    // again, I copy/pasted your code with very slight 
modifications
     string[] helper() {
             string[] targets;
             targets.length = basic_types.length;
             size_t n = 0;
             static foreach(t;basic_types)
             {
                 if (is(T : mixin(t)))
                 {
                     targets[n++] = t;
                 }
             }
             return targets[0 .. n];
     }

     mixin("alias basicTypeConvTargets = AliasSeq!(" ~ 
helper().join(",") ~ ");");
}

pragma(msg, basicTypeConvTargets!ushort);