New library: open multi-methods

[Jean-Louis Leroy via Digitalmars-d-announce]

On Tuesday, 18 July 2017 at 18:03:30 UTC, jmh530 wrote:
> On Tuesday, 18 July 2017 at 16:57:30 UTC, Ali Çehreli wrote:
>>
>> Perhaps they are all needed but I'm thinking about the need 
>> for forward declaration, the need for the underscore prefix, 
>> etc.
>>
>
> He might be able to at least get rid of the forward declaration 
> (not sure on the underscore).
>
> The way it works now is that a class that inherits from an 
> interface is not required in any way to implement the methods. 
> Suppose he adds another attribute to an interface such that any 
> class that inherits from it is required to have methods defined 
> for specific functions.
>
> So for instance, the Matrix example might look something like
>
> @trait
> interface Matrix
> {
>   @property int rows() const;
>   @property int cols() const;
>   @property double at(int i, int j) const;
>   @trait void print();
> }
>
> I'm not sure this would work because anything that derives from 
> Matrix must implement print. However, if it is possible to use 
> the attribute to allow the derived classes to ignore print, 
> then it might work. Alternately, if there is a way to process 
> the interface and tell the compiler to somehow ignore the 
> @trait member functions. I don't know if it'll work, but it's 
> an idea.
>
> Anyway, the mixin(registerMethods); could then be adjusted so 
> that void print(virtual!Matrix m); is mixed in automatically 
> because we now know how to construct it.

There are at least problems with this. Firstly it is intrusive - 
something I strive to avoid (although I could be 100% orthogonal 
only because I hijack a deprecated pointer in ClassInfo). Also, 
some methods may want to treat Matrix as a virtual argument, and 
some not.

Look at 
https://github.com/jll63/methods.d/blob/master/examples/matrix/source/matrix.d and https://github.com/jll63/methods.d/blob/master/examples/matrix/source/densematrix.d They know nothing about printing. They don't want to. The matrix modules do math, the app does printing.

J-L