various questions

[bearophile]

Simpler:

import std.stdio: writeln;
import std.typetuple: TypeTuple;

template Iota(int stop) {
    static if (stop <= 0)
        alias TypeTuple!() Iota;
    else
        alias TypeTuple!(Iota!(stop-1), stop-1) Iota;
}

void foo(T, int N, int M)() {
    writeln(typeid(T), " ", N, " ", M);
}

enum string[] types = ["int", "float", "short"];
alias TypeTuple!(int, float, short) types2;

enum string[] sizes = ["100", "200", "250"];
enum int[] sizes2 = [100, 200, 250];

void main() {
    string run_t = "int";
    string run_n = "200";
    string run_m = "100";

    foreach (t; Iota!(types.length))
        foreach (n; Iota!(sizes.length))
            foreach (m; Iota!(sizes.length))
                if (run_t == types[t] && run_n == sizes[n] && run_m == sizes[m]) {
                    foo!(types2[t], sizes2[n], sizes2[m])();
                    goto END;
                }

    END: {}
}