On Friday, 10 May 2024 at 00:18:16 UTC, Andy Valencia wrote:
tst7.d(6): Error: cannot implicitly convert expression `e in
this.members` of type `bool*` to `bool`
tst7.d(15): Error: template instance `tst7.Foo!uint` error
instantiating
I'm getting this for this bit of source (trimmed from the
bigger code). I switched to this.members.get(e, false) and
that works fine, but I'm still curious:
struct Foo(T) {
bool[T] members;
bool
has(T e) {
return (e in this.members);
}
}
void
main()
{
import std.stdio : writeln;
auto t = Foo!uint();
writeln(t.has(123));
}
Yes. The reason for this is that it avoids having to essentially
do the same check twice. If `in` returned a bool instead of a
pointer, after checking for whether the element exists (which
requires searching for the element in the associative array),
you'd then have to actually *get* it from the array, which would
require searching again. Returning a pointer to the element if it
exists (or `null` if it doesn't) cuts this down to 1 operation.
