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From: Ian Collins <ian-news@hotmail.com>
Newsgroups: comp.lang.c++
Subject: Re: mutable vs const_cast, which is better to modify field from const function?
Date: Sat, 09 Jul 2011 19:28:18 +1200
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On 07/ 9/11 06:19 PM, Qi wrote:
> It's not rare to lazy initialize member field in getter functions which
> are const function.
>
> class SomeClass {
> public:
> 	MyObject * getMyObject() const {
> 		if(! this->myObject) {
> 			this->myObject = create the object;
> 		}
> 		
> 		return this->myObject;
> 	}

You don't need all those "this->".

> private:
> 	MyObject * myObject;
> };
>
> To be able to modify myObject in the getter function, we can
> either,
> 1, Use mutable on myObject.
> mutable MyObject * myObject;
> or
> 2, Use const_cast to cast away constness from "this".
> const_cast<SomeClass *>(this)->myObject = create the object;
>
> Both methods have their own pros and cons, that's why I can't
> decide which is better.

How about:

struct SomeClass
{
   SomeClass() {}

   MyObject* getMyObject() const
   {
     static MyObject* myObject;

     if(!myObject)
     {
       myObject = new MyObject;
     }
		
     return myObject;
   }
};

-- 
Ian Collins