Chapter 8. Tweaks

Question 1

Item 41: Consider pass by value for copyable parameters that are cheap to move and always copied.

Answer 1

For copyable, cheap-to-move parameters that are always copied, pass by value may be nearly as efficient as pass by reference, it’s easier to implement, and it can generate less object code.

For lvalue arguments, pass by value (i.e., copy construction) followed by move assignment may be significantly more expensive than pass by reference followed by copy assignment.

Pass by value is subject to the slicing problem, so it’s typically inappropriate for base class parameter types.

Question 2

Item 42: Consider emplacement instead of insertion.

Answer 2

In principle, emplacement functions should sometimes be more efficient than their insertion counterparts, and they should never be less efficient.

In practice, they’re most likely to be faster when (1) the value being added is constructed into the container, not assigned; (2) the argument type(s) passed differ from the type held by the container; and (3) the container won’t reject the value being added due to it being a duplicate.

Emplacement functions may perform type conversions that would be rejected by insertion functions.