*final* class member (D2)

[Neil Vice]

"Denton Cockburn" <diboss at hotmail.com> wrote in message 
news:pan.2008.02.13.22.55.38.263151 at hotmail.com...
> On Wed, 13 Feb 2008 14:33:33 -0500, Steven Schveighoffer wrote:
>
>> "Denton Cockburn" wrote
>>> How do I do this?  I'm trying to create a class member here that needs 
>>> to
>>> be initialized in the constructor, but cannot be changed later.
>>>
>>> class A
>>> {
>>>   (const doesn't work) real delegate() dg; // this is that
>>>   function;
>>>
>>>   this(real delegate() dg) { this.dg = dg; }
>>> }
>>>
>>> class B
>>> {
>>>   real foo() { return 3.5; }
>>> }
>>>
>>> class C
>>> {
>>>   real foo() { return 4.5; }
>>> }
>>>
>>> void main()
>>> {
>>>   auto b = new B;
>>>   auto a = new A(&b.foo);
>>>   auto c = new C;
>>>   a.fitness = &c.foo; // I want this to be an error
>>> }
>>
>> um... did you try encapsulation?
>>
>> class A
>> {
>>    private real delegate() _dg;
>>
>>    public real dg()
>>    {
>>       return _dg();
>>    }
>>
>>    this(real delegate() dg) { this._dg = dg; }
>> }
>>
>> -Steve
>
> This was the workaround I used as well.
> I don't like it because of the extra level of indirection (I end up
> calling 2 functions instead of 1).  I don't consider this very efficient
> or convenient.

I would have expected the dg() method (or property I guess) in the above to 
be inlined, possibly requiring a final specifier? In that case I don't see 
any reduction in performance.

As a matter of interest the following code is fairly equivalent but results 
in some bizarre property/delegate interaction:

class A
{
    private real delegate() _dg;

    this(real delegate() dg) { this._dg = dg; }

    public real delegate() dg()
    {
        return _dg;
    }
}

// Sample usage
public void example(real delegate() dg)
{
    A test = new A(dg);
    // test.dg        - Evaluates to the delegate dg
    // test.dg()     - Also evaluates to the delegate dg
    test.dg()()      // Required to actually execute the delegate
}

Neil