Any word on the return-type const syntax?

[Walter Bright]

Janice Caron wrote:
> On 12/8/07, Walter Bright <newshound1 at digitalmars.com> wrote:
>> Janice Caron wrote:
>>> Here's a typical problem.
>>>
>>>     class MyArray(T)
>>>     {
>>>         T[] a;
>>>
>>>         T* ptr() { return a.ptr; }
>>>         const(T)* ptr() const { return a.ptr; }
>>>         invariant(T)* ptr() invariant { return a.ptr; }
>>>     }
>>>
>>> A template helps how, exactly?
>>         TransferConst!(U,T) ptr(this U)() { return a.ptr; }
> 
> There are several things I don't understand about this example. You
> seem to be suggesting that
> 
>     TransferConst!(U,T)
> 
> resolves to
> 
>     K(T)*

I should have written:
	TransferConst!(U,T*)


> The next thing I don't understand is the notation
> 
>     ptr(this U)()
> 
> How does that even parse? I'm not familiar with this means of
> specifying template parameters. What does it mean?

It means U is given the type of the 'this' pointer. This was added in 2.008.

> The third thing I don't understand is, I see no specication of the
> constancy of the member function itself. I expect to see either
> const-at-the-end, or const-at-the-start, but I see neither. Where is
> it?

It's in wherever the 'this' pointer came from, i.e. from the caller.

> And of course, my final question has to be, is this function still
> virtual?

No.

> I think my way looks most readable, but you tell me.

The larger the function body is, the less readable and more error prone 
duplicating it becomes.

> One really important point to consider is that you need EXACTLY ONE
> instantiation of the function. That is, the bytes of machine code
> which comprise the function would be identical in all three cases, and
> therefore need to exist only once. I suspect that your template idea,
> in addition to robbing me of virtuality, would also instantiate the
> function three times.

Currently, it would instantiate it three times. This is a more general 
problem, though, and there are many other instances where it happens. 
Eventually, the best solution should be in the linker being able to 
coalesce identical comdat sections.