object::emplace

Construct an element in-place.

Synopsis

template<
    class Arg>
std::pair< iterator, bool >
emplace(
    string_view key,
    Arg&& arg);

Inserts a new element into the container constructed in-place with the given argument if there is no element with the key in the container. If the insertion occurs and results in a rehashing of the container, all iterators and references are invalidated. Otherwise, they are not affected. Rehashing occurs only if the new number of elements is greater than capacity().

Complexity

Amortized constant on average, worst case linear in size().

Exception Safety

Strong guarantee. Calls to memory_resource::allocate may throw.

Return Value

A std::pair where first is an iterator to the existing or inserted element, and second is true if the insertion took place or false otherwise.

Parameters

Name	Description
`key`	The key used for lookup and insertion
`arg`	The argument used to construct the value. This will be passed as `std::forward<Arg>(arg)` to the `value` constructor.

Exceptions

Type	Thrown On
boost::system::system_error	if key is too long.