[PATCH] D49120: [libc++] P0898R3 2 of 12: Implement <concepts> header

[Arthur O'Dwyer via Phabricator via cfe-commits]

Quuxplusone added inline comments.


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Comment at: include/concepts:175
+template <class _Tp, class _Up>
+_LIBCPP_CONCEPT_DECL Same = __same_impl<_Tp, _Up> && __same_impl<_Up, _Tp>;
+
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Peanut gallery asks: From lines 166-171 it looks awfully like `__same_impl<_Tp, _Up>` is true if and only if `__same_impl<_Up, _Tp>` is true. So why bother instantiating both templates?


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Comment at: include/concepts:280
+    Constructible<_Tp, const _Tp&> && ConvertibleTo<const _Tp&, _Tp> &&
+    Constructible<_Tp, const _Tp> && ConvertibleTo<const _Tp, _Tp>;
+
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Peanut gallery notices the lack of `Constructible<_Tp, const _Tp&&>` here, and assumes it's intentional?


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Comment at: include/concepts:295
+        requires ConvertibleTo<const remove_reference_t<_Tp>&, bool>;
+        !__t1;        requires ConvertibleTo<decltype(!__t1), bool>;
+        __t1 && __t2; requires Same<decltype(__t1 && __t2), bool>;
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Peanut gallery asks: Am I correct that the instances of `ConvertibleTo<..., bool>` here could (according to the WD) be replaced with `-> bool`?  Am I correct that the instances of `Same<..., bool>` here could eventually be replaced with `-> Same<bool>` once they fix that issue you wrote a paper about?

I assume they're written like this for portability reasons.


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Comment at: include/concepts:379
+_LIBCPP_CONCEPT_DECL Invocable = requires(_Fn&& __fn, _Args&&... __args) {
+    __invoke_constexpr(static_cast<_Fn&&>(__fn), static_cast<_Args&&>(__args)...);
+};
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Does this need a `_VSTD::` for ADL reasons? (There's one in `<tuple>` that does use `_VSTD::`; there's two in `<variant>` that don't.)


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Comment at: include/concepts:394
+    CommonReference<
+        const remove_reference_t<_Tp>&,
+        const remove_reference_t<_Up>&> &&
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I'm fairly confident that `const remove_reference_t<_Tp>&` is just `const _Tp&`.


https://reviews.llvm.org/D49120