Multiple return values...

[Andrei Alexandrescu]

On 3/9/12 10:16 AM, Timon Gehr wrote:
> There are two parts, syntax and semantics.
>
> Semantics:
> D is already able to express those:
>
> template Tuple(T...){alias T Tuple;} // not the same as std.typecons.Tuple!
>
> // function with multiple return values:
> Tuple!(int,double) foo(int a, double b){
> Tuple!(int, double) result; // ok, _no imposed memory layout_
> result[0] = a; // ok
> result[1] = a+b; // ok
> return result;
> }
>
> Multiple return values are currently *disallowed explicitly*:
> DMD sez: "Error: functions cannot return a tuple"
>
> Just specify the ABI, implement the code gen, and we're done.
>
> Moot point: built-in tuples auto-flatten inside comma-separated lists.
>
> std.typecons.Tuple is a hack to circumvent the arbitrary "cannot return
> tuple from function" restriction as well as the auto-flattening.

No, it was more like an implementation of a generic tuple.

> The
> problem is that it is implemented as a struct with a built-in tuple
> member. The fact that it is a struct imposes a memory layout. This is
> just a side-effect of attempting to address the other two issues. It is
> not something that is desirable.

Why?

I don't understand what you're trying to solve, that Tuple is not good at.


Andrei