On 4/22/20 9:45 AM, WebFreak001 wrote:
> if
> f(Items.x...)
> works then what about
> f(Items.MemberTup...) ?
I would expect an expansion as Manu described, where the natural
expansion of Items becomes Items[0].MemberTup, Items[1].MemberTup, ...
And of course, tuples in tuples auto-flatten according to current D semantics.
However, there are some ambiguities that I'm not sure have been solved.
What about templates that expand to tuples? Are the results of those
tuples part of the ... expansion?
What about:
alias F!(T...) = AliasSeq!(T, T);
Consider this expansion:
alias t = AliasSeq!(int, char);
F!(F!t))...
The expansion is evaluated from the leaf upwards... your question is valid, and this is the case we've discussed quite a lot.
I'm basically just interested to run it and see what happens naturally!
Does it mean:
F!(F!int), F!(F!char)) => int, int, int, int, char, char, char, char
or does it mean:
F!(AliasSeq!(int, char, int, char))... => int, char, int, char, int,
char, int, char
In other words, what if part of the expression *creates* a tuple. Is
that the thing that gets expanded? I would have to say no, right?
Otherwise, the whole thing might be expanded and the ... trivially applied.
So that means things like (assuming G does something similar but not
identical to F:
F!(G!int)... would have to be the same as F!(G!int). This might be very
confusing to someone expecting the inner tuple to be done before the
expansion is considered.
I don't know how to DIP-ify this idea. But it definitely needs to be
talked about.
I have thought about how to discuss this in the DIP; I describe the semantic, and what happens is what happens.
This will work, and something will happen... when we implement TemplateInstance, we'll find out exactly what it is :P
What I will do is show what such a nested tuple does when code works in the DIP to instantiate TemplateInstances.
It's basically the same thing as what you showed above with: Items[0].MemberTup, Items[1].MemberTup, ...
In general, in D currently, nested tuples flatten. Evaluate from the leaf upwards. Your answer will materialise.