Objects that can be initialized but not assigned

Question

I need to create a class whose objects can be initialized but not assigned.

I thought maybe I could do this by not defining the assignment operator, but the compiler uses the constructor to do the assignment.

I need it to be this way:

Object a=1;    // OK a=1;           // Error 

How can I do it?

Answer 1

Making a const will do the trick

const Object a=1;    // OK 

Now you won't be able to assign any value to a as a is declared as const. Note that if you declare a as const, it is necessary to initialize a at the time of declaration.

Once you have declared a as const and also initialized it, you won't be able to assign any other value to a

 a=1;   //error 

Answer 2

You can delete the assignment operator:

#include <iostream> using namespace std;  struct Object {     Object(int) {}     Object& operator=(int) = delete; };  int main() {     Object a=1;    // OK     a=1;           // Error } 

Alternative Solution

You can use the explicit keyword:

#include <iostream> using namespace std;  struct Object {     explicit Object(int) {} };  int main() {     Object a(1);    // OK - Uses explicit constructor     a=1;           // Error } 

Update

As mentioned by user2079303 in the comments:

It might be worth mentioning that the alternative solution does not prevent regular copy/move assignment like a=Object(1)

This can be avoided by using: Object& operator=(const Object&) = delete;