Template Base Classes, Refering to typeof(this)

[Robert Jacques]

On Wed, 04 Nov 2009 13:35:45 -0500, Travis Boucher  
<boucher.travis at gmail.com> wrote:

> I am writing a generic vector base class.  The class implements all of  
> the operator overloads so I don't have to implement them over and over  
> and over for each type of vector class.
>
> class VectorBase(size_t S, T) {
> 	T[S] data;
>
> 	...
> }
>
> class Vector3f : VectorBase!(3, float) { ... }
>
> The problem I am having is implementing operations that can take a  
> matching vector.  I can't figure out the proper way of declaring the  
> type of input.
>
> eg.
>
> void opAssign(VectorBase!(S, T) r);
>  > function VectorBase!(3LU,float).VectorBase.opAssign identity  
> assignment operator overload is illegal
>
>
> void opAssign(this r);
>  > basic type expected, not this
>
>
> The only way I can think of handling it is to add another parameter to  
> the template declaration, eg:
>
> class VectorBase(size_t S, T, N) { ... }
> class Vector3f : VectorBase!(3, float, Vector3f) { ... }
>
> But I would like to avoid that if possible.
>
> Any hints on how to implement this so I can keep my original  
> declaration? class VectorBase(size_t S, T)

Well first, you can't overload assignment of a class to it's own type.  
(It's part of the language spec, at the bottom of the operator overload  
page IIRC) Second, I've already solved this in D2, (using structs) so let  
me know if you want code. Third, fixed sized arrays as value-type are  
coming in the next release (I think), so you could wait for that. Lastly,  
you're (probably) going to run into issues with your other operator  
overloads because of some bugs in instantiating templates inside of  
templates using template literals as opposed to types.