getMember

static struct S { auto bar(int a) { return a; } enum boolean = true; }
static struct C { alias bar = (double a) => a * 2; enum boolean = false; }

alias V = Variant!(S, C);

V x = S();
V y = C();

static assert(is(typeof(x.getMember!"bar"(2)) == Variant!(int, double)));
assert(x.getMember!"bar"(2) == 2);
assert(y.getMember!"bar"(2) != 4);
assert(y.getMember!"bar"(2) == 4.0);

// direct implementation
assert(x.bar(2) == 2);
assert(y.bar(2) != 4);
assert(y.bar(2) == 4.0);
assert(x.boolean);
assert(!y.boolean);