equivariant functions

[Andrei Alexandrescu]

Denis Koroskin wrote:
> On Mon, 13 Oct 2008 01:27:42 +0400, Denis Koroskin <2korden at gmail.com> 
> wrote:
> 
>> On Mon, 13 Oct 2008 01:17:36 +0400, Andrei Alexandrescu 
>> <SeeWebsiteForEmail at erdani.org> wrote:
>>
>>> Denis Koroskin wrote:
>>>> May I suggest one of my personal preference? Here it is:
>>>>  sameconst(char)* strstr(sameconst(char)* str1, const(char)* str2)
>>>> {
>>>>     return str2; // compile-time error. Can't cast const(char)* to 
>>>> sameconst(char)* implicitly
>>>> }
>>>
>>> I prefer my solution because it's more general and addresses more 
>>> issues than passing the qualifier out.
>>>
>>> Andrei
>>
>> Yes, my solution doesn't address clone() method return type, but I 
>> think they aren't related.
>>
>> Besides, your solution can't implement the following example, so mine 
>> is more flexible: :)
>>
>> sameconst(char)[] findPatternInS1OrS2(sameconst(char)[] s1,
>>     sameconst(char)[] s2, string needle);
> 
> 
> And also this:
> 
> class Storage
> {
>    sameconst(Foo) foo() sameconst(this) // const, invariant or none
>    {
>         return _foo;
>    }
> 
>    private Foo _foo;
> }
> 
> Your version?

class Storage
{
     typeof(this._foo) foo() const { return _foo; }
}

Please note that your version is technically identical to Walter's 
suggestion:

T foo(return const T value);

meaning that whatever qualifier value had will be returned back. Your 
solution is better visually at the obvious cost of adding a keyword, and 
let me warn again that we can't afford to add one keyword for each 
problem we solve. I believe it is more fertile to align compiler's view 
of the code with programmer expectations.


Andrei