This needs to be fixed

[Manu]

On Wed, 28 Aug 2024 at 19:46, Nick Treleaven via Digitalmars-d <
digitalmars-d at puremagic.com> wrote:

> On Sunday, 25 August 2024 at 05:07:43 UTC, Manu wrote:
> > Like, from my example above, what even IS `s.tupleof`? It's
> > some kind of
> > list of what kind of thing? Direct symbol references to members
> > of a live
> > instance?
>
> It's a symbol sequence of references to fields.
>
> ```d
> import std;
>
> struct S
> {
>      int i;
>      char c;
> }
>
> void main()
> {
>      S s = {2, 'c'};
>      ref si = s.i;
>      ref sc = s.c;
>      alias tupleof = AliasSeq!(si, sc); // same as s.tupleof
>      tupleof[0]++;
>      s.writeln();
>      assert(s.i == 3);
>
>      // this actually works
>      alias a = tupleof[0];
>      a++;
>      assert(s.i == 4);
> }
> ```
>
> So `alias e = s.tupleof[0];` could be made to work.
>
> See also: https://dlang.org/spec/template.html#lvalue-sequences.
>
> BTW I'd like to make sequences a separate spec page from
> templates really.
>
> > If s.tupleof can populate a list with that kind of thing, why
> > doesn't this
> > work:
> >
> > struct S
> > {
> >   int x, y;
> > }
> >
> > struct T
> > {
> >   S s;
> >   int i;
> >
> >   alias a = i; // works
> >   alias b = s.x; // Doesn't work? Why?
> > }
>
> `a` is a symbol alias. `b` would be an expression if it did what
> you want. Instead it's the same as `S.x`, which needs an instance
> of S to use it at runtime.
>

Not necessarily; it doesn't need to carry around the expression; it could
evaluate the resolve the expression on the spot.


> > alias b = s.tupleof[0]; // this emits a surprising error
> > message:
> >
> > error : alias `b` cannot alias an expression `AliasSeq!(s.x,
> > s.y)[0]`
> > So, that 'list' I mention; does this error message imply that
> > this list given by `tupleof` is an AliasSeq? What exactly IS an
> > AliasSeq? What is the actual set of things that it can hold?
>
> Symbols (declarations) and compile-time values. S.x is a
> declaration, s.x is a runtime value.
>
> `tupleof` is a symbol sequence of implicit ref declarations.
>

What's a 'ref'?
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