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

 

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std::inplace_vector

Member types
Member functions
inplace_vector::inplace_vector inplace_vector::~inplace_vector      inplace_vector::operator= inplace_vector::assign inplace_vector::assign_range Size and capacity inplace_vector::empty inplace_vector::size inplace_vector::max_size inplace_vector::capacity inplace_vector::resize inplace_vector::reserve inplace_vector::shrink_to_fit Iterators inplace_vector::begininplace_vector::cbegin inplace_vector::endinplace_vector::cend inplace_vector::rbegininplace_vector::crbegin inplace_vector::rendinplace_vector::crend	Element access inplace_vector::at inplace_vector::operator[] inplace_vector::front inplace_vector::back inplace_vector::data Modifiers inplace_vector::clear inplace_vector::erase inplace_vector::swap inplace_vector::insert inplace_vector::insert_range inplace_vector::emplace inplace_vector::emplace_back inplace_vector::try_emplace_back inplace_vector::unchecked_emplace_back inplace_vector::push_back inplace_vector::try_push_back inplace_vector::unchecked_push_back inplace_vector::pop_back inplace_vector::append_range inplace_vector::try_append_range (removed in C++26)
Non-member functions
erase(std::inplace_vector)erase_if(std::inplace_vector) swap(std::inplace_vector)	operator==operator<=>

 

template< class... Args > constexpr std::optional<reference> try_emplace_back( Args&&... args );		(since C++26)

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

args	-	arguments to forward to the constructor of the element
Type requirements
- T must be EmplaceConstructible into inplace_vector from std::forward<Args>(args)....

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

Feature-test macro	Value	Std	Feature
__cpp_lib_inplace_vector	202603L	(C++26)	Better return type (std::optional<reference> instead of pointer) for try_push_back and try_emplace_back

Example

Run this code

#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

emplace_back	constructs an element in-place at the end (public member function)
push_back	adds an element to the end (public member function)
append_range	adds a range of elements to the end (public member function)
try_append_range	tries to add a range of elements to the end (public member function)
unchecked_emplace_back	unconditionally constructs an element in-place at the end (public member function)
unchecked_push_back	unconditionally adds an element to the end (public member function)
pop_back	removes the last element (public member function)
back_inserter	creates a std::back_insert_iterator of type inferred from the argument (function template)