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    std::hive<T,Allocator>::unique

    From cppreference.com

    [edit template]
     
    C++
     
    Containers library
     
    std::hive
     
    template< class BinaryPredicate = std::equal_to<T> >
size_type unique( BinaryPredicate binary_pred = BinaryPredicate() );
    		(since C++26)

    Removes all consecutive duplicate elements from the container. Only the first element in each group of equal elements is left.

    Formally, for a nonempty hive, erases all elements referred to by the iterator i in the [begin() + 1, end()) for which p(*i, *(i - 1)) is true.

    Invalidates references, pointers, and iterators referring to the erased elements. If the last element in *this is erased, also invalidates the end() iterator.

    If binary_pred does not establish an equivalence relation, the behavior is undefined.

    Parameters

    p - binary predicate which returns ​true if the elements should be treated as equal.

    The signature of the predicate function should be equivalent to the following:

    bool pred(const Type1 &a, const Type2 &b);

    While the signature does not need to have const &, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1 and Type2 regardless of value category (thus, Type1 & is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy(since C++11)).
    The types Type1 and Type2 must be such that an object of type hive<T,Allocator>::const_iterator can be dereferenced and then implicitly converted to both of them. ​

    Type requirements
    -
    BinaryPredicate must meet the requirements of BinaryPredicate.

    Return value

    The number of removed elements.

    Complexity

    If empty() is true, no comparison is performed.

    Otherwise, given N as std::distance(begin(), end()):  exactly N-1 applications of the predicate p.

    Example

    Run this code
    import std;

int main()
{
    std::hive<int> c{1, 2, 2, 3, 3, 2, 1, 1, 2};
    std::println("Before unique(): {}", c);

    const auto count1 = c.unique();
    std::println("After unique():  {} ({} elements removed)", c, count1);

    c = {1, 2, 12, 23, 3, 2, 51, 1, 2, 2};
    std::println("Before unique(pred): {}", c);

    auto pred = [mod = 10](int x, int y) { return (x % mod) == (y % mod); };
    const auto count2 = c.unique(pred);
    std::println("After unique(pred):  {} ({} elements removed)", c, count2);
}

    Output: 

    Before unique(): [1, 2, 2, 3, 3, 2, 1, 1, 2]
After unique():  [1, 2, 3, 2, 1, 2] (3 elements removed)
Before unique(pred): [1, 2, 12, 23, 3, 2, 51, 1, 2, 2]
After unique(pred):  [1, 2, 23, 2, 51, 2] (4 elements removed)

    See also

    		 removes consecutive duplicate elements in a range
    (function template & algorithm function object)[edit]
    (C++20)