Expensive-to-move types are rare in modern C++ usage. If you are concerned about the cost of the move, write both overloads: void set_a(const A& a) { _a = a; } void set_a(A&& a) { _a = std::move(a); } or a perfect-forwarding setter: template <typename T> void set_a(T&& a) { _a = std::forward<T>(a); } that will … Read more
Yes to both. Pointers are passed by value as anything else. That means the contents of the pointer variable (the address of the object pointed to) is copied. That means that if you change the value of the pointer in the function body, that change will not be reflected in the external pointer that will … Read more
I think much confusion is generated by not communicating what is meant by passed by reference. When some people say pass by reference they usually mean not the argument itself, but rather the object being referenced. Some other say that pass by reference means that the object can’t be changed in the callee. Example: struct … Read more
There is one thing nobody mentioned. There is a certain GCC optimization called IPA SRA, that replaces “pass by reference” with “pass by value” automatically: https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html (-fipa-sra) This is most likely done for scalar types (eg. int, double, etc), that does not have non-default copy semantics and can fit into cpu registers. This makes void(const … Read more
Java always passes arguments by value, NOT by reference. In your example, you are still passing obj by its value, not the reference itself. Inside your method changeName, you are assigning another (local) reference, obj, to the same object you passed it as an argument. Once you modify that reference, you are modifying the original … Read more
A good way to find out why there are any differences is to check the disassembly. Here are the results I got on my machine with Visual Studio 2012. With optimization flags, both functions generate the same code: 009D1270 57 push edi 009D1271 FF 15 D4 30 9D 00 call dword ptr ds:[9D30D4h] 009D1277 8B … Read more
Here is my own contribution for the Java programming language. first some code: public void swap(int x, int y) { int tmp = x; x = y; y = tmp; } calling this method will result in this: int pi = 3; int everything = 42; swap(pi, everything); System.out.println(“pi: ” + pi); System.out.println(“everything: ” + … Read more
Because the array is being passed by value, an exact copy of the array is made and placed on the stack. This is incorrect: the array itself is not being copied, only a copy of the pointer to its address is passed to the callee (placed on the stack). (Regardless of whether you declare the … Read more
As Rytmis said, Java passes references by value. What this means is that you can legitimately call mutating methods on the parameters of a method, but you cannot reassign them and expect the value to propagate. Example: private void goodChangeDog(Dog dog) { dog.setColor(Color.BLACK); // works as expected! } private void badChangeDog(Dog dog) { dog = … Read more
See “Slices: usage and internals” var av = []int{1,5,2,3,7} That is a slice, not an array. A slice literal is declared just like an array literal, except you leave out the element count. That explains why the sort function will modify the content of what is referenced by the slice. As commented below by Kirk, … Read more