AK: Use Deducing this for OptionalBase

[Hendiadyoin1]

This is taken from and akin to
SerenityOS/serenity#25894

---

This greatly reduces the code duplication and is a bit more strict about forwarding

[gmta]

@Hendiadyoin1 CI is failing :-(

[Hendiadyoin1]

Yeah, probably need to bump the ci compiler version

[ADKaster]

If it doesn't build with Xcode 16.3 clang, we're gonna have to hold off on this. @BertalanD , wanna try this out on the latest Xcode 26 preview? Looks like beta 3 came out a week ago

[Hendiadyoin1]

Ah whoops mainly forgot to remove a now superfluous thing
This should work on Xcode16.3 as that did bump the clang version to "17", which is actually LLVM 19
https://en.wikipedia.org/wiki/Xcode#cite_ref-208

[BertalanD]

Can confirm that Xcode 26 beta 3 (clang-1700.3.13.4) successfully builds this.

[alimpfard]

🤔 what's the point of this? AddConst<T const> is just T const anyway
This name is really confusing, I think the intent is CopyConst<RemoveReference<Self>, T> but to keep T = U const as const if Self isn't const?

regardless the && !IsConst<T> is unnecessary, AddConst is idempotent for T const.

[Hendiadyoin1]

Ah, good looked at AddConst and did not see any special handling for T const, good to know that it is idempotent anyway
And yes this is supposed to be CopyConstButDontRemoveItPls

[alimpfard]

maybe a different name then, AddConstFrom<F, T> maybe?

template<typename From, typename To>
struct AddConstFrom {
    using Type = Conditional<IsConst<RemoveReference<From>>, T, AddConst<T>>;
};

the RemoveReference bit seems a bit odd to me, but probably okay.