Assignment of tuples

[Steven Schveighoffer]

On 5/20/20 8:17 AM, Russel Winder wrote:
> So I have an enum:
> 
>     enum RC5Command: Tuple!(ubyte, ubyte) {
>         Standby = tuple(to!ubyte(0x10), to!ubyte(0x0c)),
>         …
> 
> I can do:
> 
>     RC5Command rc5command = RC5Command.CD;
> 
> However, if I do:
> 
>     rc5command = RC5Command.BD;
> 
> I get:
> 
> source/functionality.d(80,16): Error: template std.typecons.Tuple!(ubyte, ubyte).Tuple.opAssign cannot deduce function from argument types !()(RC5Command), candidates are:
> /usr/lib/ldc/x86_64-linux-gnu/include/d/std/typecons.d(900,19):        opAssign(R)(auto ref R rhs)
>    with R = RC5Command
>    must satisfy the following constraint:
>         areCompatibleTuples!(typeof(this), R, "=")
> 
> which is totally unreasonable. And yet D insists. I guess there is an
> explanation, but mostly this seems like a bug.
> 

The issue is that it's not EXACTLY a Tuple, because it's a derived type. 
So it fails isTuple (In fact, I think the compiler just isn't smart 
enough to detect that it can be implicitly converted to a Tuple).

But that defeats a lot of wrapping mechanisms, which I think is unnecessary.

I think there should probably be an overload:

opAssign(Tuple t) {expand = t.expand;}

that trumps the template one. That should I think take care of it.

Please file an issue.

-Steve