C++ Logo

STD-PROPOSALS

Advanced search

Subject: Re: [std-proposals] Operator functions to fix ADL
From: Dusan Jovanovic (DBJ) (dbj_at_[hidden])
Date: 2020-10-13 18:16:14


>* ADL is used whenever you write*
* std::string s;*
* auto t = s + s; // ADL on operator+*
* std::cout << s; // ADL on operator<<*
* swap(s, s); // ADL on swap*

*In particular, the "std::swap two-step" is used inside all swap-based STL
algorithms, such as std::rotate and std::sort.*
*So you can't actually turn it off, because then you'd break the world
(because approximately every C++ program depends on ADL somewhere). But you
could issue a warning about it outside of system headers, just to get a
sense of the magnitude of the issue.*

*> -Arthur*

*Perhaps this is why I have written "not-a-minority not using std lib" :)
... you know those pesky C++ projects using -fno-exceptions or even using
things like EASTL (gasp! again). I am not a "just-say-no-to-adl" zealot, I
am just developing your very same idea further. Let's see where that takes
us. Perhaps that might lead to some solution about removing the heavy
technical debt of ADL.*

*Enough said, peace *

*DBJ*

On Tue, 13 Oct 2020 at 21:30, Arthur O'Dwyer <arthur.j.odwyer_at_[hidden]>
wrote:

> On Tue, Oct 13, 2020 at 10:57 AM Dusan Jovanovic (DBJ) <dbj_at_[hidden]>
> wrote:
>
>> A.O.D. has written: -- I'd be interested to see a compiler patch to warn
>> whenever "ADL lookup occurred, on a non-operator, and ADL found a
>> best-matching candidate which would *not* have been found by regular
>> unqualified lookup." It couldn't be used in production because
>> approximately every C++ program depends on ADL *somewhere*. But it could
>> give us a sense of the magnitude of the issue. --
>>
>> Why not just going further: *-fno-adl*
>>
>> That would certainly "rock the boat". In my not-a-compiler-writer
>> naivete, I might think, contrary to A.O.D. (gasp!) a lot of code will
>> work unbroken with that switch.? Especially that silent not-minority not
>> using std lib.
>>
>
> ADL is used whenever you write
> std::string s;
> auto t = s + s; // ADL on operator+
> std::cout << s; // ADL on operator<<
> swap(s, s); // ADL on swap
>
> In particular, the "std::swap two-step" is used inside all swap-based STL
> algorithms, such as std::rotate and std::sort.
> So you can't actually turn it *off*, because then you'd break the world
> (because approximately every C++ program depends on ADL *somewhere*). But
> you could issue a warning about it outside of system headers, just to get a
> sense of the magnitude of the issue.
>
> -Arthur
>



STD-PROPOSALS list run by std-proposals-owner@lists.isocpp.org

Standard Proposals Archives on Google Groups