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Subject: Re: [std-proposals] Generic template 'this'
From: Jake Arkinstall (jake.arkinstall_at_[hidden])
Date: 2020-03-08 17:03:22


For me, this approach has some merits, but this particular example is
something that, to me, makes much more sense as a free function.

Do you have further examples?

On Sun, 8 Mar 2020, 21:55 Phil Bouchard via Std-Proposals, <
std-proposals_at_[hidden]> wrote:

> Well I believe a proposal should be open for debate, just like a thesis.
>
> We both agree these overloads should be simplified but we disagree on the
> syntax.
>
> I saw the recursive lambda thing and I think I already talked to you
> before regarding CV overloads but we were proposing the following syntax:
>
> struct A
>
> {
>
> template <bool BC>
>
> void foo() bool<BC>
>
> {
>
> }
>
> };
>
> And regarding the this generic overloading I still believe the following
> syntax is cleaner:
>
> struct A
>
> {
>
> template <typename T>
>
> bool compare(T const &);
>
> };
>
> template <typename C, typename T>
>
> void C::compare(C const &)
>
> {
>
> ...
>
> }
>
> Because with your syntax I could technically reassign "self":
>
> struct A
>
> {
>
> template <typename C, typename T>
>
> bool compare(this C & c, T const &);
>
> };
>
> template <typename C, typename T>
>
> bool C::compare(this C & c, T const &) // redundant C here
>
> {
>
> static C sc = C();
>
> c = sc; // in theory we could do this unless you patch the
> compilers with a new error for that specific case
>
> }
>
>
> --
>
> *Phil Bouchard*
> Founder
> C.: (819) 328-4743
>
> [image: Fornux Logo] <http://www.fornux.com>
>
>
> On 3/8/20 5:37 AM, Gašper Ažman wrote:
>
> I meant that you should consider the incremental value of your proposal
> over p0847, which is on track for c++23 unless serious issues crop up
>
> On Sat, Mar 7, 2020, 19:04 Phil Bouchard <phil_at_[hidden]> wrote:
>
>> The syntaxes are way different:
>>
>> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p0847r4.html
>>
>> In your case the compiler will have to change all of its rules for the
>> number of parameters "operator" overloads. For example:
>>
>> struct A
>>
>> {
>>
>> int value;
>>
>> ...
>>
>> template <typename Self>
>>
>> bool operator < (this Self && self, A const & a) // 2
>> parameters... ok
>>
>> {
>>
>> return self.value < a.value;
>>
>> }
>>
>>
>> bool operator < (A const & a) // 1 parameter... ok
>>
>> {
>>
>> return value < a.value;
>>
>> }
>>
>> };
>>
>>
>> --
>>
>> *Phil Bouchard*
>> Founder
>> C.: (819) 328-4743
>>
>> [image: Fornux Logo] <http://www.fornux.com>
>>
>>
>> On 3/7/20 1:35 PM, Gašper Ažman wrote:
>>
>> P0847
>>
>> On Sat, Mar 7, 2020, 18:33 Phil Bouchard via Std-Proposals <
>> std-proposals_at_[hidden]> wrote:
>>
>>> Alright, I'm pretty sure this is not implemented yet. Suppose you have:
>>>
>>> struct A
>>>
>>> {
>>>
>>> int value;
>>>
>>> ...
>>>
>>> template <typename T>
>>>
>>> int compare(T const & t) const;
>>>
>>> }
>>>
>>>
>>> struct B
>>>
>>> {
>>>
>>> int value;
>>>
>>> ...
>>>
>>> template <typename T>
>>>
>>> int compare(T const & t) const;
>>>
>>> }
>>>
>>>
>>> Then a generic way to define the same functionality for all classes
>>> would be to have a "template 'this'":
>>>
>>> template <typename C, typename T>
>>>
>>> inline int C::compare(T const & t) const
>>>
>>> {
>>>
>>> return value == t.value ? 0 : value < t.value ? -1 : 1;
>>>
>>> }
>>>
>>>
>>> (Please include my email address in your replies)
>>>
>>>
>>> --
>>>
>>> *Phil Bouchard*
>>> Founder
>>> C.: (819) 328-4743
>>>
>>> [image: Fornux Logo] <http://www.fornux.com>
>>> --
>>> Std-Proposals mailing list
>>> Std-Proposals_at_[hidden]
>>> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals
>>>
>> --
> Std-Proposals mailing list
> Std-Proposals_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals
>



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