equivariant functions

[Steven Schveighoffer]

"Andrei Alexandrescu" wrote
> Steven Schveighoffer wrote:
>> "Andrei Alexandrescu" wrote
>>> I discussed with Walter a variant that implements equivariant functions 
>>> without actually adding an explicit feature to the language. Consider:
>>>
>>> typeof(s) stripl(const(char)[] s);
>>
>> As another point on this, I think someone else mentioned it, but I can't 
>> find the post.
>>
>> I don't like the way this looks.  The way it reads is 'stripl returns the 
>> same type as s', but really, the typeof(s) is actually modifying the type 
>> of the argument also.  This seems very unintuitive.
>
> I agree. We need to look for a better notation.
>
>> I understand the need to not change the language, but I think most would 
>> prefer a syntax where the type modifier is specified on at least the 
>> argument.  People are going to be extremely confused when they can't 
>> treat 's' like a normal const(char)[].
>>
>> If the ultimate result is that no intuitive syntax can be made without 
>> changing the language, then I think it is more important to have this 
>> feature than to not change the language.
>>
>> One other syntax that Janice proposed (and I later put into a bugzilla), 
>> is to use the dead keyword inout.  Meaning, what you send in is what you 
>> get out.  ref already completely replaces inout, so there is no need to 
>> keep it under its current meaning:
>>
>> inout(char)[] stripl(inout(char)[] s);
>>
>> I'm not in love with this completely, but it has the benefit of not 
>> requiring a new keyword.
>
> Also I guess:
>
> class C
> {
>     Range!(inout(C)) foo() inout;
> }
>
> And also:
>
> class Base {}
> class Derived : Base {}
> inout foo(inout Base b);

In this last example, what does the inout mean at the front?

> I think this could work and doesn't look half bad. Of course, you'll be 
> tasked with addressing protests about yet another D1/D2 incompatibility. 
> :o)

inout is obsolete in D1 also.  The answer to the protest is 'change inout to 
ref.'  At some point, you can make inout invalid in D1, so it doesn't have a 
double meaning.

Not a big deal IMO ;)

-Steve