Re: Pattern matching via switch?

[aliak via Digitalmars-d-learn]

On Saturday, 14 March 2020 at 19:04:28 UTC, 12345swordy wrote:
I.E.
switch (object)
    case Type1 t1:
    case Type2 t2:
    case Type3 t3:

You can use the sumtype package 
(https://code.dlang.org/packages/sumtype):

alias T = SumType!(Type1, Type2, Type3);

T(object).match!(
    (Type1 t1) => "t1",
    (Type2 t2) => "t2",
    (Type3 t3) => "t3",
);


Or you can make a quick template like:

template switch_(funs...) {
    auto switch_(T)(auto ref T t) {
        static foreach (fun; funs) {
            static if (is(typeof(fun(T.init)))) {
                return fun(t);
            }
        }
    }
}

struct A {}
struct B {}
struct C {}

void main()
{
    auto a = C();
    a.switch_!(
        (A _) => "a",
        (B _) => "b",
        (C _) => "c",
    ).writeln;
}

The template above is a quick fix and will have some holes 
though. Off the top of my head if more than one lambda "fits" 
there'll be problems.