Expand scope of a variable initialized in a if/else sequence

Question

I\'m writing a piece of code in which I\'d like to use a different constructor of a class depending on a condition. So far I\'ve used if and else s

Answer 1

If you want to use a variable outside of a given scope, it must be declared outside that scope.

void foo()
{
    MyClass my_object;
    if (my_boolean){
        my_object = MyClass(arg1); //calling a first constructor,
                                   //then copy or move assignment
    }
    else {
        my_object = MyClass(arg1,arg2); //calling another constructor,
                                   //then copy or move assignment
    }
    //more code using my_object
}
//Can no longer access my_object

If you want to do it this way, I suggest defining a move assignment operator if the default will not work for your purposes (or there isn't a default move assignment operator).

Also, the code where you are using my_object may be cleaner if you move the if/else blocks and object construction to a separate function, then do something like:

MyClass my_object = make_object(my_boolean);

Or, if arg1 and arg2 aren't global,

MyClass my_object = make_object(my_boolean, arg1, arg2);

If creating an object gets more complicated than what you've asked about here, you may wish to look into the factory pattern.