template<class... Args> std::pair<iterator, bool> emplace(Args&& ... args);
Inserts a new element into a JSON object constructed in-place with the given args if there is no element with the key in the container. If the function is called on a JSON null value, an empty object is created before appending the value created from args.
Args : compatible types to create a basic_json object
args (in) : arguments to forward to a constructor of basic_json
a pair consisting of an iterator to the inserted element, or the already-existing element if no insertion happened, and a #!cpp bool denoting whether the insertion took place.
Throws type_error.311 when called on a type other than JSON object or #!json null; example: "cannot use emplace() with number"
Logarithmic in the size of the container, O(log(size())).
??? example
The example shows how `emplace()` can be used to add elements to a JSON object. Note how the `#!json null` value was
silently converted to a JSON object. Further note how no value is added if there was already one value stored with
the same key.
```cpp
--8<-- "examples/emplace.cpp"
```
Output:
```json
--8<-- "examples/emplace.output"
```