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Re: ambiguous reference to 'find' in std and std::ranges namespaces

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On 2022-04-13 at 13:27, Paavo Helde wrote:
> 13.04.2022 10:58 Ralf Goertz kirjutas:
>> Hi,
>>
>> why do I get the error (with gcc-Version 11.2.1):
>>
>>
>> find_test.cc: In function ‘int main()’:
>> find_test.cc:10:41: error: reference to ‘find’ is ambiguous
>>     10 |     std::vector<int>::const_iterator it=find(v,47);
>>        |                                         ^~~~
>>
>> when compiling the following code:
>>
>> #include <algorithm>
>> #include <ranges>
>> #include <vector>
>>
>> using namespace std;         // *
>> using namespace std::ranges; // **
>>
>> int main() {
>>      const std::vector<int> v({47,11});
>>      std::vector<int>::const_iterator it=find(v,47);
>> }
> 
> Most probably this is because std::ranges::find is not a function 
> template, but something called "niebloid", to disable ADL 
> ("https://en.cppreference.com/w/cpp/algorithm/ranges/find").
> 
> In my implementation it appears to be implemented as a function object, 
> having operator() member functions. I guess the problem is caused by 
> this specific implementation, as the whole point of niebloids seems to 
> be the opposite (avoiding clashes with the std:: namespace).

That works from *inside* the ranges namespace. Once an object is found, 
the compiler knows not to do ADL, because that's only for functions.

> 
>> AFAICT there is no way that std::find could be a candidate whereas
>> std::ranges::find matches. 
> 
> I guess the compiler never gets so far as to consider template overload 
> candidates.

It cannot do that when the candidates are not all functions. There are 
no overload rules for objects (like niebloids).

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ambiguous reference to 'find' in std and std::ranges namespaces Ralf Goertz <me@myprovider.invalid> - 2022-04-13 09:58 +0200
  Re: ambiguous reference to 'find' in std and std::ranges namespaces Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-13 14:27 +0300
    Re: ambiguous reference to 'find' in std and std::ranges namespaces Bo Persson <bo@bo-persson.se> - 2022-04-13 14:21 +0200
      Re: ambiguous reference to 'find' in std and std::ranges namespaces Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-13 15:31 +0300
    Re: ambiguous reference to 'find' in std and std::ranges namespaces Juha Nieminen <nospam@thanks.invalid> - 2022-04-13 13:26 +0000
      Re: ambiguous reference to 'find' in std and std::ranges namespaces Juha Nieminen <nospam@thanks.invalid> - 2022-04-13 13:28 +0000
        Re: ambiguous reference to 'find' in std and std::ranges namespaces Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-13 17:26 +0300
        Re: ambiguous reference to 'find' in std and std::ranges namespaces Christian Gollwitzer <auriocus@gmx.de> - 2022-04-14 07:13 +0200
          Re: ambiguous reference to 'find' in std and std::ranges namespaces Ralf Goertz <me@myprovider.invalid> - 2022-04-14 08:57 +0200
            Re: ambiguous reference to 'find' in std and std::ranges namespaces Bo Persson <bo@bo-persson.se> - 2022-04-14 13:23 +0200
              Re: ambiguous reference to 'find' in std and std::ranges namespaces Paavo Helde <eesnimi@osa.pri.ee> - 2022-04-14 16:32 +0300
                Re: ambiguous reference to 'find' in std and std::ranges namespaces Bo Persson <bo@bo-persson.se> - 2022-04-14 18:30 +0200
              Re: ambiguous reference to 'find' in std and std::ranges namespaces Ralf Goertz <me@myprovider.invalid> - 2022-04-15 10:14 +0200
            Re: ambiguous reference to 'find' in std and std::ranges namespaces Manfred <noname@add.invalid> - 2022-04-14 15:02 +0200
  Re: ambiguous reference to 'find' in std and std::ranges namespaces Christian Hanné <the.hanne@gmail.com> - 2022-04-15 14:39 +0200

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