operator==(std::common_iterator)

Since C++20

Compares the iterators and/or sentinels held by underlying std::variant member objects var. Two incomparable iterators or two sentinels are considered equal.

# Declarations

template <class I2, std::sentinel_for<I> S2>
requires std::sentinel_for<S, I2>
friend constexpr bool operator==( const common_iterator& x,
const std::common_iterator<I2, S2>& y );

(since C++20)

template <class I2, std::sentinel_for<I> S2>
requires std::sentinel_for<S, I2> && std::equality_comparable_with<I, I2>
friend constexpr bool operator==( const common_iterator& x,
const std::common_iterator<I2, S2>& y );

(since C++20)

# Parameters

x, y: iterator adaptors to compare

# Return value

true if underlying iterators and/or sentinels are equal.

# Example

#include <cassert>
#include <iterator>
 
int main()
{
    int a[]{0, 1, 2, 3};
 
    using CI = std::common_iterator<
                   std::counted_iterator<int*>,
                   std::default_sentinel_t
                   >;
 
    CI i1{std::counted_iterator{a + 0, 2}};
    CI i2{std::counted_iterator{a + 1, 2}};
    CI i3{std::counted_iterator{a + 0, 3}};
    CI i4{std::counted_iterator{a + 0, 0}};
    CI s1{std::default_sentinel};
    CI s2{std::default_sentinel};
 
    assert((i1 == i2) == true);
    assert((i1 == i3) == false);
    assert((i2 == i3) == false);
    assert((s1 == s2) == true);
    assert((i1 == s1) == false);
    assert((i4 == s1) == true);
}

# Defect reports

DR	Applied to	Behavior as published	Correct behavior
LWG 3574	C++20	variant was fully constexpr (P2231R1) but common_iterator was not	also made constexpr

# See also

operator-