std::inplace_vector<T,N>::try_emplace_back

template< class... Args >
constexpr std::optional<reference> try_emplace_back( Args&&... args );

Conditionally appends an object of type T to the end of the container.

If size() == capacity() is true, there are no effects. Otherwise, appends direct-non-list-initialized with std::forward<Args>(args)... object of type T.

No iterators or references are invalidated, except end(), which is invalidated if the insertion occurs.

Parameters

Return value

std::nullopt if size() == capacity(), std::optional<reference>(std::in_place, back()) otherwise.

Complexity

Constant.

Exceptions

Any exception thrown by initialization of inserted element. If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee).

Notes

Example

#include <cassert>
#include <complex>
#include <inplace_vector>
#include <optional>

int main()
{
    using namespace std::complex_literals;
    using C = std::complex<double>;
    using I = std::inplace_vector<C, 3>;
    auto v = I{1.0 + 2.0i, 3.0 + 4.0i};

    std::optional<C&> c = v.try_emplace_back(5.0, 6.0);
    assert(*c == 5.0 + 6.0i);
    assert((v == I{1.0 + 2.0i, 3.0 + 4.0i, 5.0 + 6.0i}));

    c = v.try_emplace_back(7.0, 8.0); // no space => no insertion
    assert(c == std::nullopt);
    assert((v == I{1.0 + 2.0i, 3.0 + 4.0i, 5.0 + 6.0i}));
}

See also