Make deque iterator operators hidden friends

[François Dumont]

Thanks for the tip, nice to know.

Attached patch applied.

François

On 5/8/19 8:28 PM, Jonathan Wakely wrote:
> On 08/05/19 18:50 +0200, François Dumont wrote:
>> Here is a patch to reduce number of operators exposed at std 
>> namespace scope.
>>
>> Â Â Â  * include/bits/stl_deque.h
>> Â Â Â  (_Deque_iterator<>::operator+(difference_type)): Make hidden friend.
>> Â Â Â  (_Deque_iterator<>::operator-(difference_type)): Likewise.
>> Â Â Â  (operator==(const _Deque_iterator<>&, const _Deque_iterator<>&)):
>> Â Â Â  Likewise.
>> Â Â Â  (operator!=(const _Deque_iterator<>&, const _Deque_iterator<>&)):
>> Â Â Â  Likewise.
>> Â Â Â  (operator<(const _Deque_iterator<>&, const _Deque_iterator<>&)):
>> Â Â Â  Likewise.
>> Â Â Â  (operator<=(const _Deque_iterator<>&, const _Deque_iterator<>&)):
>> Â Â Â  Likewise.
>> Â Â Â  (operator>(const _Deque_iterator<>&, const _Deque_iterator<>&)):
>> Â Â Â  Likewise.
>> Â Â Â  (operator>=(const _Deque_iterator<>&, const _Deque_iterator<>&)):
>> Â Â Â  Likewise.
>>
>> Tested under Linux x86_64 normal/debug modes.
>>
>> Ok to commit ?
>>
>> François
>>
>
>> diff --git a/libstdc++-v3/include/bits/stl_deque.h 
>> b/libstdc++-v3/include/bits/stl_deque.h
>> index 7a7a42aa903..72420c27646 100644
>> --- a/libstdc++-v3/include/bits/stl_deque.h
>> +++ b/libstdc++-v3/include/bits/stl_deque.h
>> @@ -238,24 +238,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
>> Â Â Â Â return *this;
>> Â Â Â Â Â  }
>>
>> -Â Â Â Â Â  _Self
>> -Â Â Â Â Â  operator+(difference_type __n) const _GLIBCXX_NOEXCEPT
>> -Â Â Â Â Â  {
>> -Â Â Â  _Self __tmp = *this;
>> -Â Â Â  return __tmp += __n;
>> -Â Â Â Â Â  }
>> -
>> Â Â Â Â Â  _Self&
>> Â Â Â Â Â  operator-=(difference_type __n) _GLIBCXX_NOEXCEPT
>> Â Â Â Â Â  { return *this += -__n; }
>>
>> -Â Â Â Â Â  _Self
>> -Â Â Â Â Â  operator-(difference_type __n) const _GLIBCXX_NOEXCEPT
>> -Â Â Â Â Â  {
>> -Â Â Â  _Self __tmp = *this;
>> -Â Â Â  return __tmp -= __n;
>> -Â Â Â Â Â  }
>> -
>
> These two are already not visible at namespace-scope, but it doesn't
> hurt to make them hidden friends for consistency.
>
>> +Â Â Â Â Â  friend _Self
>> +Â Â Â Â Â  operator+(const _Self& __x, difference_type __n) 
>> _GLIBCXX_NOEXCEPT
>> +Â Â Â Â Â  {
>> +Â Â Â  _Self __tmp = __x;
>> +Â Â Â  return __tmp += __n;
>
> I know you've just reused the original implementation, but it has a
> problem that we might as well fix while touching t his code.
>
> This function prevents NRVO copy elision, because __tmp += __n returns
> a reference, which gets copied into the return value.
>
> If you write it like this then the copy is elided, and __tmp is
> constructed directly in the return value slot:
>
> Â _Self __tmp = __x;
> Â __tmp += __n;
> Â return __tmp;
>
>
>> +Â Â Â Â Â  friend _Self
>> +Â Â Â Â Â  operator-(const _Self& __x, difference_type __n) 
>> _GLIBCXX_NOEXCEPT
>> +Â Â Â Â Â  {
>> +Â Â Â  _Self __tmp = __x;
>> +Â Â Â  return __tmp -= __n;
>
> Same problem here. It would be better to write:
>
> Â _Self __tmp = __x;
> Â __tmp -= __n;
> Â return __tmp;
>
> OK for trunk with those two changes, thanks.
>
>
>

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