Const again

[naryl]

On Sun, 27 Jan 2008 18:17:03 +0300, Jason House  
<jason.james.house at gmail.com> wrote:

> naryl wrote:
>
>> Is there a way to make something like this work in D 2.0?
>>
>> clone is supposed to make a new shallow copy of it's object:
>>
>>   interface Cloneable
>>   {
>>       const Cloneable clone();
>>   }
>>
>>   class Demo : Cloneable
>>   {
>>       public :
>>           this(){}
>>
>>           this( Demo reference )
>>           {
>>               reference_ = reference;
>>           }
>>
>>           override const Demo clone() {
>>               return new Demo( reference_ );
>>           }
>>       private:
>>           Demo reference_;
>>   }
>>
>>   void main()
>>   {
>>       auto a = new Demo(new Demo);
>>       auto b = a.clone();
>>   }
>>
>> The method clone must be const and there must be a non-const constructor
>> in Demo.
>
> It looks like you should change this( Demo reference ) to this( const  
> Demo
> reference ).  Is that what you were saying is not allowed?  If so, can  
> you
> explain what's going wrong and why you can't?

Never mind. Shallow clone() cannot be const because reference_ may be  
changed through it's copy. The problem was solved by making two versions:  
"Demo clone()" and "const Demo deepClone()":

class Demo
{
         public :
                 this(){}

                 public this(Demo reference) {
                         reference_ = reference;
                 }

                 Demo clone() {
                         if (reference_ !is null)
                                 return new Demo( reference_ );
                         else return new Demo();
                 }

                 const Demo deepClone() {
                         if (reference_ !is null)
                                 return new Demo( reference_.deepClone() );
                         else return new Demo();
                 }

         private:
                 Demo reference_;
}