Revised RFC on range design for D2 (lazy)

[Fawzi Mohamed]

On 2008-10-03 12:05:17 +0200, Bruno Medeiros 
<brunodomedeiros+spam at com.gmail> said:

> Andrei Alexandrescu wrote:
>> Sean Kelly wrote:
>>> == Quote from Andrei Alexandrescu (SeeWebsiteForEmail at erdani.org)'s article
>>>> Bruno Medeiros wrote:
>>>>> I don't understand that. You stated "It violates economy of syntax.", so
>>>>>  it violates your Principle 1 of language design. So how can you be
>>>>> happy with that (apart from the assignment issue)? Does fixing this
>>>>> problem violate some other principle or concern of yours?
>>>> I think keeping the language simple is also a good goal.
>>> 
>>> I apologize if this has been brought up before, but I'm not sure that 
>>> simplicity
>>> is a good thing if it can result in unpredictable behavior.  For example:
>>> 
>>>     import std.stdio;
>>> 
>>>     class C
>>>     {
>>>         this( bool delegate() p )
>>>         {
>>>             version( a )
>>>                 cond = p;
>>>             version( b )
>>>                 ptr = p;
>>>         }
>>>         version( a )
>>>         {
>>>             bool delegate() cond;
>>>         }
>>>         version( b )
>>>         {
>>>             bool delegate() ptr;
>>>             bool delegate() cond() { return ptr; }
>>>         }
>>>     }
>>> 
>>>     void main()
>>>     {
>>>         bool test() { writefln( "hi" ); return false; }
>>>         auto c = new C( &test );
>>>         if( c.cond() )
>>>             writefln( "true" );
>>>     }
>>> 
>>> Running version=a prints "hi" while version=b prints "true."  If there were
>>> some way in the language to say "cond() is a property" then this issue would
>>> not be silently introduced when changing cond from a variable to a method.
>> 
>> Oh how I am with you on this. I've always thought mentioning a delegate 
>> name should NOT EVER evaluate the delegate. Walter definitely took the 
>> wrong turn down that alley there. And guess what. He got ambushed by 
>> the "lazy" keyword right there. I told Walter to not do that "lazy" 
>> keyword, he disregarded, but the time will come when that stone will be 
>> turned.
>> 
>> 
>> Andrei
> 
> Hold it right there! Are you saying that the existence of 'lazy' 
> somehow required, or helped justify the existence of the omittable 
> parenthesis functionality? How is that?
> I think you are accusing innocents ('lazy') or wrongdoing. 'lazy' has 
> nothing to do with the omittable parenthesis functionality, I think 
> they are completely orthogonal. Prove me wrong otherwise.

I think that he meant that lazy automatically evaluates a delegate, and 
that he thinks it is wrong.
He said it because he thought that the problem shown by Sean was 
connected with automatically evaluating a delegate, which it is not, 
but let's not start another sub-thread...

Fawzi