template<class... Args> reference emplace_back(Args&& ... args);
Creates a JSON value from the passed parameters args to the end of the JSON value. If the function is called on a JSON #!json null value, an empty array 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
reference to the inserted element
Throws type_error.311 when called on a type other than JSON array or #!json null; example: "cannot use emplace_back() with number"
Amortized constant.
??? example
The example shows how `emplace_back()` can be used to add elements to a JSON array. Note how the `null` value was
silently converted to a JSON array.
```cpp
--8<-- "examples/emplace_back.cpp"
```
Output:
```json
--8<-- "examples/emplace_back.output"
```