equivariant functions

[Andrei Alexandrescu]

Denis Koroskin wrote:
> On Mon, 13 Oct 2008 01:52:25 +0400, Andrei Alexandrescu 
> <SeeWebsiteForEmail at erdani.org> wrote:
> 
>> Denis Koroskin wrote:
>>> Sorry to hit a dead horse but...
>>>  auto dg = &stripl; // what is the type of dg?
>>
>> stripl is three overloads. You must use a precise type on the 
>> receiving side to get a pointer to function, as with any overloaded 
>> symbol.
>>
>>> string z = dg("foo");
>>> char[] x = dg("foo".dup);
>>>  It is great that you brought the issue to discussion, but I think 
>>> this solution is a miss.
>>
>> I'm glad you're trying to dent it, this is the best way to find bugs 
>> in it. But let me note that so far you haven't gotten even near :o).
>>
>>
>> Andrei
> 
> Ok, I'll try harder. Here is a common used pattern:
> 
> interface IMaybeBar
> {
>     Bar isBar();
>     const(Bar) isBar();
>     invariant(Bar) isBar();
> }
> 
> class Foo : IMaybeBar
> {
>     Bar isBar() { return null; }
>     const(Bar) isBar() const { return null; }
>     invariant(Bar) isBar() invariant { return null; }
> }
> 
> class Bar : Foo
> {
>     Bar isBar() { return this; }
>     const(Bar) isBar() const { return this; }
>     invariant(Bar) isBar() invariant { return this; }
> }
> 
> let's change it into one.
> 
> interface IMaybeBar
> {
>     same(Bar) isBar() same(this); // same is shorter than sameconst and 
> as descriptive as sameconst
> }
> 
> class Foo
> {
>     same(Bar) isBar() same(this) { return null; }
> }
> 
> class Bar : Foo
> {
>     same(Bar) isBar() same(this) { return this; }
> }
> 
> Your solution? Note that it shouldn't conflict with your clone example:
> 
>> class S
>> {
>>      typeof(this) clone();
>> }

Walter found an answer last night.

interface IMaybeBar
{
     Bar isBar();
     const(Bar) isBar() const;
     invariant(Bar) isBar() invariant;
}

class Foo : IMaybeBar
{
     PassQual!(typeof(this), Bar) isBar() const { return null; }
}

class Bar : Foo
{
     typeof(this) isBar() const { return this; }
}


Andrei