Topic: pointer that propagates it's modifiers to the value
Author: Alexey Mamontov <caracrist@gmail.com>
Date: Mon, 22 Aug 2016 10:54:37 -0700 (PDT)
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The idea is simple. I need to have some member by pointer (using the
abstract base class, for example), but I want it to behave absolutely the
same as member by value - it must inherit the constantness of this.
Lets call it member_ptr<T> and see what I mean:
T * member_ptr<T>::operator->();
const T * member_ptr<T>::operator->() const;
T & member_ptr<T>::operator*();
const T & member_ptr<T>::operator*() const;
struct B
{
void f() = 0;
void f() const = 0;
};
struct S
{
member_ptr<B> m;
};
S s;
s.m->f(); // void f() is called
const S cs;
cs.m->f(); // void f() const is called
All other modifiers (volatile, rvalue) must be forwarded as well...
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<div dir=3D"ltr"><div>The idea is simple.=C2=A0I need to have some member b=
y pointer (using the abstract base class, for example), but I want it to be=
have absolutely the same as member by value - it must inherit the constantn=
ess of this.</div><div><br></div><div>Lets call it member_ptr<T> and =
see what I mean:</div><div><div><br></div><div>T *=C2=A0member_ptr<T>=
::operator->();</div><div>const T * member_ptr<T>::operator->()=
const;<div><br></div><div>T & member_ptr<T>::operator*();</div><=
div>const T=C2=A0& member_ptr<T>::operator*() const;</div><div><b=
r></div><div>struct B</div><div>{</div><div>=C2=A0void f() =3D 0;</div><div=
>=C2=A0void f() const =3D 0;</div><div>};</div><div>struct S</div><div>{</d=
iv><div>=C2=A0member_ptr<B> m;</div><div>};</div><div><br></div><div>=
S s;</div><div>s.m->f(); // void f() is called<div>const S cs;</div><div=
>cs.m->f(); // void f() const is called</div><div><br></div><div>All oth=
er modifiers (volatile, rvalue) must be=C2=A0forwarded as well...=C2=A0</di=
v></div></div></div></div>
<p></p>
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Author: Shahms King <shahms.king@gmail.com>
Date: Mon, 22 Aug 2016 18:11:34 +0000
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http://en.cppreference.com/w/cpp/experimental/propagate_const
--Shahms
On Mon, Aug 22, 2016 at 10:54 AM Alexey Mamontov <caracrist@gmail.com>
wrote:
> The idea is simple. I need to have some member by pointer (using the
> abstract base class, for example), but I want it to behave absolutely the
> same as member by value - it must inherit the constantness of this.
>
> Lets call it member_ptr<T> and see what I mean:
>
> T * member_ptr<T>::operator->();
> const T * member_ptr<T>::operator->() const;
>
> T & member_ptr<T>::operator*();
> const T & member_ptr<T>::operator*() const;
>
> struct B
> {
> void f() = 0;
> void f() const = 0;
> };
> struct S
> {
> member_ptr<B> m;
> };
>
> S s;
> s.m->f(); // void f() is called
> const S cs;
> cs.m->f(); // void f() const is called
>
> All other modifiers (volatile, rvalue) must be forwarded as well...
>
> --
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> .
>
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<div dir=3D"ltr"><a href=3D"http://en.cppreference.com/w/cpp/experimental/p=
ropagate_const">http://en.cppreference.com/w/cpp/experimental/propagate_con=
st</a><br><div><br></div><div>--Shahms</div></div><br><div class=3D"gmail_q=
uote"><div dir=3D"ltr">On Mon, Aug 22, 2016 at 10:54 AM Alexey Mamontov <=
;<a href=3D"mailto:caracrist@gmail.com">caracrist@gmail.com</a>> wrote:<=
br></div><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;borde=
r-left:1px #ccc solid;padding-left:1ex"><div dir=3D"ltr"><div>The idea is s=
imple.=C2=A0I need to have some member by pointer (using the abstract base =
class, for example), but I want it to behave absolutely the same as member =
by value - it must inherit the constantness of this.</div><div><br></div><d=
iv>Lets call it member_ptr<T> and see what I mean:</div><div><div><br=
></div><div>T *=C2=A0member_ptr<T>::operator->();</div><div>const =
T * member_ptr<T>::operator->() const;<div><br></div><div>T & =
member_ptr<T>::operator*();</div><div>const T=C2=A0& member_ptr&l=
t;T>::operator*() const;</div><div><br></div><div>struct B</div><div>{</=
div><div>=C2=A0void f() =3D 0;</div><div>=C2=A0void f() const =3D 0;</div><=
div>};</div><div>struct S</div><div>{</div><div>=C2=A0member_ptr<B> m=
;</div><div>};</div><div><br></div><div>S s;</div><div>s.m->f(); // void=
f() is called<div>const S cs;</div><div>cs.m->f(); // void f() const is=
called</div><div><br></div><div>All other modifiers (volatile, rvalue) mus=
t be=C2=A0forwarded as well...=C2=A0</div></div></div></div></div>
<p></p>
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</blockquote></div>
<p></p>
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Author: Jonathan Coe <jonathanbcoe@gmail.com>
Date: Mon, 22 Aug 2016 22:23:05 +0200
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> On 22 Aug 2016, at 20:11, Shahms King <shahms.king@gmail.com> wrote:
>
> http://en.cppreference.com/w/cpp/experimental/propagate_const
>
libc++ and libstd++ both have implementations in trunk.
Please let me know if they don't do what you want.
The libc++ implementation should work pretty easily in VS without significant modification.
> --Shahms
>
>> On Mon, Aug 22, 2016 at 10:54 AM Alexey Mamontov <caracrist@gmail.com> wrote:
>> The idea is simple. I need to have some member by pointer (using the abstract base class, for example), but I want it to behave absolutely the same as member by value - it must inherit the constantness of this.
>>
>> Lets call it member_ptr<T> and see what I mean:
>>
>> T * member_ptr<T>::operator->();
>> const T * member_ptr<T>::operator->() const;
>>
>> T & member_ptr<T>::operator*();
>> const T & member_ptr<T>::operator*() const;
>>
>> struct B
>> {
>> void f() = 0;
>> void f() const = 0;
>> };
>> struct S
>> {
>> member_ptr<B> m;
>> };
>>
>> S s;
>> s.m->f(); // void f() is called
>> const S cs;
>> cs.m->f(); // void f() const is called
>>
>> All other modifiers (volatile, rvalue) must be forwarded as well...
>> --
>> 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.
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>
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<html><head><meta http-equiv=3D"content-type" content=3D"text/html; charset=
=3Dutf-8"></head><body dir=3D"auto"><div></div><div><br></div><div><br>On 2=
2 Aug 2016, at 20:11, Shahms King <<a href=3D"mailto:shahms.king@gmail.c=
om">shahms.king@gmail.com</a>> wrote:<br><br></div><blockquote type=3D"c=
ite"><div><div dir=3D"ltr"><a href=3D"http://en.cppreference.com/w/cpp/expe=
rimental/propagate_const">http://en.cppreference.com/w/cpp/experimental/pro=
pagate_const</a><br><div><br></div></div></div></blockquote><div><br></div>=
<div>libc++ and libstd++ both have implementations in trunk.</div><div><br>=
</div><div>Please let me know if they don't do what you want.</div><div><br=
></div><div>The libc++ implementation should work pretty easily in VS witho=
ut significant modification.</div><br><blockquote type=3D"cite"><div><div d=
ir=3D"ltr"><div>--Shahms</div></div><br><div class=3D"gmail_quote"><div dir=
=3D"ltr">On Mon, Aug 22, 2016 at 10:54 AM Alexey Mamontov <<a href=3D"ma=
ilto:caracrist@gmail.com">caracrist@gmail.com</a>> wrote:<br></div><bloc=
kquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #cc=
c solid;padding-left:1ex"><div dir=3D"ltr"><div>The idea is simple. I =
need to have some member by pointer (using the abstract base class, for exa=
mple), but I want it to behave absolutely the same as member by value - it =
must inherit the constantness of this.</div><div><br></div><div>Lets call i=
t member_ptr<T> and see what I mean:</div><div><div><br></div><div>T =
* member_ptr<T>::operator->();</div><div>const T * member_ptr=
<T>::operator->() const;<div><br></div><div>T & member_ptr<=
T>::operator*();</div><div>const T & member_ptr<T>::opera=
tor*() const;</div><div><br></div><div>struct B</div><div>{</div><div> =
;void f() =3D 0;</div><div> void f() const =3D 0;</div><div>};</div><d=
iv>struct S</div><div>{</div><div> member_ptr<B> m;</div><div>};=
</div><div><br></div><div>S s;</div><div>s.m->f(); // void f() is called=
<div>const S cs;</div><div>cs.m->f(); // void f() const is called</div><=
div><br></div><div>All other modifiers (volatile, rvalue) must be forw=
arded as well... </div></div></div></div></div>
<p></p>
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