equivariant functions

[Denis Koroskin]

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();
> }