Funny thing is, I am learning Zig at the moment and had to do just that and was impressed at how clean the solution was:

    const my_enum = enum {
        one,
        two,
        three,

        pub fn str(self: @This()) []const u8 {
            return switch (self) {
                inline else => |tag| @tagName(tag),
            };
        }
    }

Inline else means the switch/case is expanded at compile time.