Two questions about assignments

[Kenji Hara]

On Tuesday, 28 May 2013 at 00:29:04 UTC, bearophile wrote:
>> std.typecons.Tuple supports "structural assignment" before the 
>> change.
>> The code also works with 2.062.
>
> I know it's not a regression. But you say:
> "Named-field tuple should be a subtype of unnamed-field tuple."
>
> You can have sub-typing, or you can have structural typing, but 
> mixing the two "silently" seems a mess.
>
> Also in your test cases of that commit fdcaba7226c... there is:
>
> +    Tuple!(int, int)[] arr;
> +    arr ~= tuple(10, 20); // OK
> +    arr ~= Tuple!(int, "x", int, "y")(10, 20); // NG -> OK
>
> If I try to do the opposite, that is to append a tuple(10, 20) 
> to an array of tuples with named fields, I get an error:
>
> import std.typecons;
> void main() {
>     Tuple!(int, "x", int, "y")[] arr;
>     arr ~= tuple(10, 20); // Error.
> }
>
>
> So here there is a true sub-typing. So sometimes tuples with 
> named fields are sub-types and in other situations they act in 
> a structural typing way. I think this mix of behaviours is a 
> little confusing.

Basically Tuple would follow structural typing. Even if it is 
impossible, it would follow true subtyping right now. That's the 
purpose of my change.

Kenji Hara