actually what you propose was in the motivation of the paper introducing ref-qualification of member functions.

I started to teach to lvalue-ref qualify user-declared  assignment operators.

but changing the standard library and the language might be too much of a change with not too much of a benefit that it would be worthwhile attempting. (I have thought proposing it)

Regards
Peter

sent from a mobile device so please excuse strange words due to autocorrection.
Peter Sommerlad
peter.cpp@sommerlad.ch
+41-79-432 23 32

> On 28 Jul 2021, at 18:34, Paul Raffer via Std-Proposals <std-proposals@lists.isocpp.org> wrote:
>
> 
> Another proposal idea:
>
>
> I think in most setters (and other methods that modify an object like operator=) in the standard library (e.g. the setters real and imag in the complex class) the this-pointer should be lvalue ref-qualified, so that temporary objects can't be modyfied.
>
> The signature of real should look like this
> constexpr void real(T value) &;
> instead of this
> constexpr void real(T value);
>
>
> In C++20 code like this
> std::complex<double>{}.real(42.0);
> or this
> std::complex<double>{} = std::complex<double>{};
> would compile, but makes no sense.
>
>
> That could potentially break existing code, but only code that has bugs anyway. So that's a feature not a bug. Or am I wrong?
>
>
> Paul
>
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