User function that is called to map an
item of the original model to
an item expected by the map model.
The returned items must conform to the item type of the model they are used with.
The item to map.
The called function takes ownership of the data, and is responsible for freeing it.
The argument can be
The data is owned by the caller of the function.
The item to map to.
|The caller of the function takes ownership of the data, and is responsible for freeing it.|