fix issue 21187 - allow to alias directly .tupleof

[ghost]

It is actually not a good idea to use .tupleof[index] because the whole tuple is regenerated for each use.
But for now alias id = T.tupleof is not allowed which is odd so this PR allows the alias, without using an AliasSeq

To advocate the change, note that the problem was noticed several times over the past years:

• "BTW, AliasSeq!(x.tupleof) is redundant, x.tupleof is already an AliasSeq", Steven Schveighoffer, 2017
• "The explicit AliasSeq should not be necessary, since the tupleof already is one", Jonathan M Davis, 2017.

[dlang-bot]

Thanks for your pull request, @NilsLankila!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	21187	enhancement	.tupleof should be directly usable as alias

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#11604"

[PetarKirov]

I suggest changing this example to:

Suggested change

	alias thisTup = typeof(this).tupleof;
	alias thisTup = this.tupleof;

as accessing this.{a, b, c, d} through a type looks quite confusing. I don't know if it's late to change this, but I'd expect that only this.tupleof (or .tupleof on any object instance (class or struct, doesn't matter)) would be able to access instance members.

typeof(this).tupleof should, of course, continue working, but I expect it to only yield static info about the type - a sequnece of types, (and their names and default values) and not a direct reference to struct/class object members.

[ghost]

No I did the right thing, what you propose is even an error since a few release (this or super used as a type)

Error: Using this as a type is obsolete. Use typeof(this) instead

[ghost]

BTW when this is required, the compiler can rewrite a VarExp /CallExp to a DotVarExp that adds the missing this.

[PetarKirov]

Error: Using this as a type is obsolete. Use typeof(this) instead

I'm aware of https://github.com/dlang/dmd/pull/9711/files, however I think it's a bug to get this error here, as in this context, typeof(this).tupleof should be equivalent to F.tupleof, which I don't see how it could be allowed to reference instance (non-static) members. Whether you access typeof(this) inside of a class or struct, or F.tupleof (where F is their name for example) from outside must have the same semantics in the same module (I don't want
to get into private / protected, but for now even in different modules).

[ghost]

I don't see how it could be allowed to reference instance (non-static) members

but .tupleof doesn't even return static members

[RazvanN7]

I'm gonna close this as the author has abandoned it. Anyone can pick it up.