is there any specific case where pass-by-value is preferred over pass-by-const-reference in C++?

Question

I read that they are conceptually equal. In practice, is there any occasion that

foo(T t) 

is preferred over

foo(const T&         


        

Answer 1

Another case that hasn't been mentioned is heavy use of the object. Let's say you pass a struct with 5 ints as members. If you are going to be accessing all 5 quite a lot in your function, there comes a point when the dereference cost outweighs the copy cost. However, you'd have to run a profiler to know when that is.

I should point out, though, that things like STL containers, which allocate memory on the heap, should almost never be passed by value if avoidable, because heap allocation is very slow compared to stack allocation.