Clause 20: Try to use reference-to-constent instead when passing objects, Pass-by-value

Note that in the case of C + +, the underlying compiler, the reference type is often implemented by pointers, so pass-by-reference is often passed a pointer, which is often a bit more expensive to pass a reference for C + + built-in types. But this cannot be a reason for not using pass-by-reference for all small objects.

Summary:

1. Try to replace Pass-by-value with Pass-by-reference-to-const, which is not only more efficient, but also avoids cutting problems

2. These rules do not apply to built-in types, STL iterators, and Function objects , which are more appropriate for these kinds of pass-by-value.

Clause 20: Try to use reference-to-constent instead when passing objects, Pass-by-value