[C++11] Emplacement vs. Insert

Scott Meyers - The evolving search for effective C++ - Keynote @ Meeting C++ 2014

Emplacement vs. Insert

• Emplacement most likely win if:
• Value being added is constructed into the container , not assigned.
• i.e The chunk of space has never being constructed before, i.e
• vector.resize doesn't count, since resize default construct the spot with constructed type T
• inserting in the middle, also not qualified.
• Argument(s) passed are different from T.
• i.e It's a Direct initialization from constructor, not copy constructor.
• Value to be added is unlikely to be rejected as a duplicate.
• i.e For unique key containers. Otherwise, it will first emplace construct the node, compare, and toss away the node since this key already exist in the container.
• Insertion respects explicit constructor, emplacement does not.