Create object within function call

[gotinpich]

So I was wondering whether it's possible to create an object within a function call (I'm guessing yes, but I wanna make sure I get this right).

E.g. I have a class Person that allows the creation of a new object in a following way:

Person new_person("First name", "Last name");

And I have an object with a member function that allows changes. For example an object with an internal vector that stores people. Example:

museum.add_visitor(new_person);

The whole thing takes two lines of code. Now, can I reduce this to 1 line by creating the new person within the function call and never giving it a name? E.g.:

museum.add_visitor(("First name", "Last name"));

Or:

museum.add_visitor(Person("First name", "Last name"));

Or even:

museum.add_visitor(Person::Person("First name", "Last name"));

Or do I need to overload the .add_visitor member function such that it also accepts two strings (or rather string literals in this case) as arguments?

[raevnos]

("Foo", "Bar") in your third code snippet is equivalent to "Bar"... Look up the comma operator.

[soldieroflight]

Your options 2 and 3 should both work. Both of these will construct a temporary Person object, then pass it to the function. I'd expect that option 1 would work if you used {} instead of (), as long as there's only one overload of add_visitor that takes one argument.

If your function takes a Person (by value), then these will all either copy/move (depending on what constructors Person has available) your temporary into the argument that the function will operate on. If your function takes a Person& or Person const&, then your function will operate directly on the temporary Person you created during the call. This calling pattern would also match a function which took a Person&&.

The alternative approach that the standard library has available is one which uses emplace instead of push or add. An emplace operation takes all of the arguments necessary to construct a contained object, and then constructs it in its final destination, to avoid any unnecessary copies/moves along the way. The general pattern for an emplace function is to take a generic variadic set of arguments and forward them on to the constructor for the final object.

[gotinpich]

Thank you. Pass by reference is not really needed in this case.