Associative arrays in D and default comparators

[Ivan Senji]

Walter Bright wrote:
> Ivan Senji wrote:
>> Yes: here is a suggestion: remove opCmp from Object. I think the only 
>> reason it is there is that when AAs where first implemented templates 
>> weren't where they are now so there was no way to check if an object 
>> has opCmp. These days a template version of AAs would be much better, 
>> and it would (if I'm not mistaken) remove the need for opCmp to be in 
>> Object.
> 
> While it'd be fun to offer a templated version of AAs, I feel the core 
> capabilities should be available to the user without needing templates. 
> This is because many programmers are not comfortable with them.

I didn't mean change int[char[]] to AA!(int, char[]),
I meant it would be nice to change the implementation to a template, 
without changing the syntax.

I guess this is one thing in D I still can't get over the C++ way.
(a couple of years back I thought iostream and <<, >> where the best :)
But these AAs and their requirements are bugging me: Why do I have to 
(in my class ABC) declare opCmp to be int opCmp(Object o)?
IMO that sucks because when used in an AA it's not like there is going 
to be objects of different types as keys.

And that is a textbook example of when a template should be used.


> 
> Can you give an example of a class that could not have a meaningful 
> opCmp implementation that one would want to put into an AA?

Sean Kelly gave a good example.

But I have nothing against AAs requiring opCmp, opEquals, toHash or what 
ever it needs, but would prefer for them not to be in Object.