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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c++
Subject: Re: I think references should have been const by default
Date: Sat, 23 Oct 2021 15:07:16 -0700
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Bart <bc@freeuk.com> writes:
> On 23/10/2021 13:23, Ben Bacarisse wrote:
>> David Brown <david.brown@hesbynett.no> writes:
>> 
>>> I think it is odd, however, that you can have qualified types in the
>>> generic association list, since they can't ever match anything
>>> (AFAICS).
>> I was curious so I tried this:
>>    #include <stdio.h>
>>        struct S { const int i; } s;
>>    struct S f(void) { return s; }
>>        int main(void)
>>    {
>>         const char *t =
>>              _Generic(f().i,
>>                             int:       "int",
>>                       const int: "const int");
>>         puts(t);
>>    }
>> f().i is not a lvalue and has a const-qualified type.  gcc prints
>> "int",
>> but clang prints "const int".  I think clang is right here.  (So much
>> for "they all copy gcc"!)
>
> You need to file a bug report to Clang's developers so that they can
> fix that oversight!
>
> But, why do think Clang is wrong? The type has a top-level const qualifier.
>
> I don't get why this is only removed for an lvalue (where you'd think
> that a const attribute is more critical).

The removal of type qualifiers is part of lvalue conversion.  No lvalue,
no lvalue conversion.

I can see that it would make sense for the expression `f().i` to have
type int rather than const int, but the standard doesn't say so.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips
void Void(void) { Void(); } /* The recursive call of the void */