220 35788 <383622f1-4c62-4af6-b684-c3d0fdcd3b9c@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Does guaranteed elision breaks bit_cast? 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The concern is what happens with this: int i = ...; float *f = new(&i) auto(bit_cast(i)); Well, the rules of guaranteed elision require that the prvalue returned by `bit_cast` directly initializes the object. And that object's storage is the same as the parameter passed to `bit_cast`. So... how exactly does that work? Is this just something that is just for implementers to worry about? Or should there be standard wording to explicitly forbid this? -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/383622f1-4c62-4af6-b684-c3d0fdcd3b9c%40isocpp.org. ------=_Part_578_1276454921.1512589411209 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
The new `bit_cast` feature voted into C++20 allows yo= u to do this:

int i =3D ...;
float j =3D= bit_cast&= lt;float>i);
<= /code>

Assuming the two types have the same size.<= /div>

The concern is what happens with this:
<= br>
int i =3D ...;=
float<= /span> *f =3D new(&i) auto(bit_cast<float>(i));

Well, the rules of guaranteed elision require that the prvalue return= ed by `bit_cast` directly initializes the object. And that object's sto= rage is the same as the parameter passed to `bit_cast`.

So... how exactly does that work? Is this just something that is just= for implementers to worry about? Or should there be standard wording to ex= plicitly forbid this?

--
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