On Sat, 7 Jan 2023 at 21:16, Lénárd Szolnoki via Std-Discussion <
std-discussion_at_[hidden]> wrote:

> Hi,
>
> [over.best.ics.general]:
>
> "Implicit conversion sequences are concerned only with the type,
> cv-qualification, and value category of the argument and how these are
> converted to match the corresponding properties of the parameter."
>
>
> https://timsong-cpp.github.io/cppwp/n4868/over.match#over.best.ics.general-2
>
> My reading is that the intent of this paragraph is to specify that
> viable and best viable functions are selected based on only type + cv +
> value category of arguments, and disregard any other property. (This
> probably only applies to expression arguments, as initializer list
> arguments have non of these properties, but this is just a tangent.)
>
> One example is that a call like `foo(some_obj.bit_field)` could find
> `foo(int&)` as viable, and later become ill-formed if this turns out to
> be the best viable function for the call.
>
> However this same paragraphs rules out to consider whether the argument
> is a null-pointer constant or not. Based on this a call like `foo(0)`
> shouldn't find `foo(void *)` viable, as there is no implicit conversion
> sequence from a prvalue of type int to `void *`,
>

Yes, by https://wg21.link/conv.ptr#1 .


> Is this a defect in the standard?
>

Probably, yes. This could almost be an editorial fix, hedging just a little:

Implicit conversion sequences are concerned only with the type,
> cv-qualification, and value category of the argument and how these are
> converted to match the corresponding properties of the parameter.
> <https://eel.is/c++draft/over.best.ics.general#2.sentence-1>[*Note 1
> <https://eel.is/c++draft/over.best.ics.general#note-1>*: *Most *
> other properties, such as the lifetime, storage class, alignment,
> accessibility of the argument, whether the argument is a bit-field, and
> whether a function is deleted <https://eel.is/c++draft/dcl.fct.def.delete>,
> are ignored. <https://eel.is/c++draft/over.best.ics.general#2.sentence-2>
>
> So, although an implicit conversion sequence can be defined for a given
> argument-parameter pair, the conversion from the argument to the parameter
> might still be ill-formed in the final analysis.
> <https://eel.is/c++draft/over.best.ics.general#2.sentence-3>
> — *end note*]


Still, best to run it past CWG. Are you OK to open an issue at
https://github.com/cplusplus/CWG/issues ?