On Tuesday, 17 August 2021 at 19:53:52 UTC, james.p.leblanc wrote:
On Tuesday, 17 August 2021 at 19:44:29 UTC, H. S. Teoh wrote:
You could use a helper template and an AliasSeq for this:
template isAmong(T, S...) {
static if (S.length == 0)
enum isAmong = false;
else
enum isAmong = is(T == S) ||
isAmong(T, S[1..$]);
}
import std.meta : AliasSeq;
alias MyTypes = AliasSeq!(int, float, MySpecialStruct);
auto myFunc(T)(T a, T b) if (isAmong!(T, MyTypes)) { ... }
T
Dear H.S. Teoh,
Wow! That is absolutely beautiful ... I had never seen (or even
imagined) a recursive template! This expands my mind in a good
way ... and is going into my toolbox immediately.
Best Regards,
James
FYI: in this particular case, you can use std.meta.staticIndexOf
instead of writing the recursion out yourself:
import std.meta: staticIndexOf;
enum isAmong(T, S...) = staticIndexOf!(T, S) >= 0;
Docs: https://phobos.dpldocs.info/std.meta.staticIndexOf.html
