On Wed, 12 Feb 2025, 02:07 Александр Поваляев, <apovalyaev_at_[hidden]> wrote:

> *[[[[My comments in bold]]]]*
>
> вт, 11 февр. 2025 г. в 22:04, Jonathan Wakely <cxx_at_[hidden]>:
>
>>
>>
>> On Tue, 11 Feb 2025 at 18:33, Александр Поваляев via Std-Proposals <
>> std-proposals_at_[hidden]> wrote:
>>
>>> *[[[My comments in bold]]]*
>>>
>>> вт, 11 февр. 2025 г. в 21:06, Bo Persson via Std-Proposals <
>>> std-proposals_at_[hidden]>:
>>>
>>>> On tis 2025-02-11 at 09:29, Александр Поваляев via Std-Proposals wrote:
>>>> > A Proposal to Add a New Multiset container Method to the Standard
>>>> > Library Technical Report
>>>> >
>>>>
>>>> > C++ Containers library std::multiset
>>>> >
>>>> > (1) size_type reduce( const Key& key );
>>>> >
>>>> > (2)
>>>> > template< class K >
>>>> > size_type reduce( K&& x );
>>>> >
>>>> > (3) size_type reduce( const Key& key, size_type count );
>>>> >
>>>> > (4)
>>>> > template< class K >
>>>> > size_type reduce( K&& x, size_type count );
>>>> >
>>>> > This method acts in right the opposite way to how method 'insert'
>>>> does.
>>>> > Method 'reduce' decreases the number of std::multiset elements with
>>>> > the same key value. And while being supplied within the second
>>>> argument
>>>> > 'size_type count', method 'reduce' decreases the number of
>>>> std::multiset
>>>> > elements with the same key value but several times.
>>>> >
>>>>
>>>> How do we know if the function is to remove the oldest or the newest
>>>> inserts? Or some in the middle?
>>>>
>>> *[[[Aleksandr]]] I believe it should be in the priority queue like
>>> style. *
>>>
>>
>> No, there is no priority here.
>>
>>
>>> *https://en.cppreference.com/w/cpp/container/multiset
>>> <https://en.cppreference.com/w/cpp/container/multiset> says "*
>>>
>>> *The order of the elements that compare equivalent is the order of
>>> insertion and does not change.*
>>> *(since C++11)**", so the oldest inserts should be deleted.*
>>>
>>
>> It doesn't say anything about "oldest". You cannot know which are the
>> "oldest", you can only know which are the closest to the beginning of the
>> container.
>>
>> If you insert every equivalent element using a hint, you can put the
>> newer elements before the older ones, or after them. So the order of
>> equivalent elements is not in oldest to newest, or newest to oldest. It
>> depends on how they were inserted.
>>
>
> [[[[Aleksandr]]]] "The order of the elements that compare equivalent is
> the order of insertion and does not change" (
> https://en.cppreference.com/w/cpp/container/multiset) means that an
> element which is inserted first will be the closest to the beginning of the
> container amongst all the elements with the same key value.
>

That's not always true, because you can use a hint when inserting.

s.insert(s.insert(1), 1);

This inserts two equivalent elements and the newer one is closer to the
beginning.



And so, it will be the first element to be deleted by a 'reduce' method
> call.
>
Let's call such an element as "oldest" amongst all the elements within the
> same key value.
>