D mixins

[BCS]

Ary Manzana wrote:
> janderson escribió:
>> Lutger wrote:
>>> janderson wrote:
>>>> I'm trying to explain to a friend on msn what mixins are.  Can you
>>>> provide some good examples, that would be difficult otherwise?
>>>>
>>>> -Joel
>>>
>>> What about implementing multiple inheritance in a language that does 
>>> not have multiple inheritance? (interface + mixin as default 
>>> implementation)
>>
>> Thanks for your reply.
>>
>> Well coming from C++ this would not make much sense.  Where would you 
>> use them in C++?  Where would you use them in D?  Are there any good D 
>> examples that show the power of mixins in a simple way that would be 
>> more ugly another way?
>>
>> Cheers.
>> -Joel
> 
> The singleton pattern is a nice and real world example of some use for 
> mixins:
> 
> # template Singleton() {
> #
> #    protected static typeof(this) _instance;
> #    protected this() { }
> #
> #    public static typeof(this) instance() {
> #        if (!_instance) {
> #            _instance = new typeof(this)();
> #        }
> #        return _instance;
> #    }
> #
> # }
> 
> And you use it like this:
> 
> # class MySingletonClass {
> #
> #     mixin Singleton!();
> #
> # }
> 
> I believe mixins are just to save you from writing bolierplate code, I 
> don't know if there are other uses...
> 
> Ary

With the use of tuples and static foreach, they can also be used to 
insert generated code into a scope. this is handy if the generated code 
needs to access user defined code

I just posed about an example of this (and a lot more template work) 
over in digitalmars.D.announce "D Template based paser generator in 137 
loc".