TIP (5 minute read): remainder on const objects

[Valmont]

Recap On const Methods

A const method is to be declared if this method is not allowed to modify the pointer this.

Example:

class AClass
{
public:
  //Must implement a constructor otherwise no const(ant) instance is allowed.
  AClass() {}
  void DoStuffNonConst()
  {
  }
  void DoStuffConst() const
  {
  }
};

DoStuffConst() won't be allowed to modify any members.
So far the recap.

Enforcing const(ness) of objects

One may want to create and intialize a const object:

const AClass theConstObject;

To enforce the constness of this object, this object may only call const methods:

class AClass
{
public:
  //Must implement a constructor otherwise no const(ant) instance is allowed.
  //Remember, const objects *must* be intialized. Hence the constructor.
  AClass() {}
  void DoStuffNonConst()
  {
  }
  void DoStuffConst() const
  {
  }
};

int main()
{
  const AClass theConstObject;
  theConstObject.DoStuffNonConst(); // ILLEGAL.
  theConstObject.DoStuffConst(); // LEGAL.
 
  return 0;
}

[Valmont]

Well since you all had time to get used to this, here is a little homework assignment:\

Using the class in the first thread add pointer of type double as the internal representation.
1) Now define a member "double* DoStuffConst() const" in such a way, so this pointer can be modified after all. You may not use casts.
2) What is the lesson you learned?