On 19/04/2022 10:37, Edward Catmur wrote:
> On Tue, 19 Apr 2022 at 03:22, <language.lawyer_at_[hidden]> wrote:
>
>> On 18/04/2022 23:23, Edward Catmur wrote:
>>> On Mon, 18 Apr 2022 at 21:13, <language.lawyer_at_[hidden]> wrote:
>>>
>>>> On 18/04/2022 22:57, Edward Catmur wrote:
>>>>> I suppose that paragraph <
>> https://eel.is/c++draft/expr.call#7.sentence-4>
>>>> (and
>>>>> the following Note) should be struck entirely.
>>>> I'd say then we will not know which object [expr.prim.this]/1 speaks
>> about
>>>> («The keyword `this` names a pointer to the object for which an implicit
>>>> object member function is invoked»)
>>>>
>>>
>>> "the object for which an implicit object member function is invoked"
>> seems
>>> clear enough; per [expr.call]/2 it's the object expression on the LHS of
>>> the postfix expression (before the '.', '->', '.*' or '->*').
>>
>> If it is a base-class function, the object is the corresponding base class
>> subobject, isn't it?
>>
>
> Yes, but that's a problem with [expr.prim.this]/1; you can't have a pointer
> of base type pointing to an object of derived type. So that subclause is
> also defective, and should have appended ", or to its base class subobject,
> as appropriate".

I don't understand where the defect is.
When «the object for which function is invoked» is a base class subobject (and it is pointed to by `this`), there is no discrepancy between the type of `this` and the object's type.
«The object for which function is invoked» does not have to be «the result of the object expression».

> As for [expr.call]/7, there's no need to specify *how* the implementation
> is expected to come up with the value of the `this` pointer (although it
> could be a Note).

When you say that [expc.call]/2 defines the object for which the function is invoked, do you mean «the call is as a member of the class object referred to by the object expression»?
  
> e.g.:
>
> --- a/source/expressions.tex
> +++ b/source/expressions.tex
> @@ -1198,7 +1198,8 @@
> \indextext{\idxcode{this}}%
> The keyword \keyword{this} names a pointer to the object for which an
> implicit object member
> function\iref{class.mfct.non.static} is invoked or a non-static data member's
> -initializer\iref{class.mem} is evaluated.
> +initializer\iref{class.mem} is evaluated, or to its base class
> +subobject\iref{class.derived}, as appropriate.
>
> \pnum
> The \defnadj{current}{class} at a program point is
> @@ -3197,12 +3198,12 @@
> int x = f<int>(); // error: no argument for second
> function parameter
> \end{codeblock}
> \end{example}
> -If the function is an implicit object member
> -function, the \keyword{this} parameter of the function\iref{expr.prim.this}
> -is initialized with a pointer to the object of the call, converted
> -as if by an explicit type conversion\iref{expr.cast}.
> \begin{note}
> -There is no access or ambiguity checking on this conversion; the access
> +If the function is an implicit object member
> +function, within the function the \keyword{this}\iref{expr.prim.this}
> +names a pointer to the object of the call or to its base class subobject
> +as appropriate, as if converted by an explicit type conversion\iref{expr.cast}.
> +There is no access or ambiguity checking on this (notional)
> conversion; the access
> checking and disambiguation are done as part of the (possibly implicit)
> class member access operator.
> See~\ref{class.member.lookup}, \ref{class.access.base},
>