无法分配一个指向模板化类的指针的成员

Question

My problem is that in my "Widget" class i've the following declaration:

MouseEvent* X;

In a member function I initialize the pointer with an address the normal way:

X = new MouseEvent;

Ok, this last line makes the compiler stop at:

error C2166: l-value specifies const object

All right, a MouseEvent is declared as a typedef to simplify things:

typedef Event__2<void, Widget&, const MouseEventArgs&> MouseEvent;

And Event__2 is, as you may imagine as: (basic structure shown):

template <typename return_type, typename arg1_T, typename arg2_T>
class Event__2
{
     ...
};

I don't know where the Event__2 class gets the const qualifier. Any tips ?

Thanks.

Answer 1

Likely, the member function where you are initializing X is marked as const - something like this.

class Foo
{
   int *Bar;

public:

   void AssignAndDoStuff() const
   {
      Bar = new int; // Can't assign to a const object.
      // other code
   }
}

The solution here is either to

1. Assign to Bar in a separate non-const method,
2. change AssignAndDoStuff to be non-const, or
3. mark Bar as mutable .

Pick one of the above:

class Foo
{
   mutable int *Bar; // 3

public:
   void Assign() // 1
   {
       Bar = new int; 
   }   
   void DoStuff() const
   {
       // Other code
   }

   void AssignAndDoStuff() // 2
   {
      Bar = new int; 
      // other code
   }
}