Different libraries offering similar functionality often feature different performance trade-offs, so we might be able to remove bottlenecks by replacing one library with another.

Assignment versions of operators (such as operator+=) tend to be more efficient than stand-alone versions of those operators (e.g., operator+).

Overloading to avoid temporaries.

Take use of the return value optimization in compilers.

Unnamed non-heap objects are invisible temporary objects in C++.