Revised RFC on range design for D2

[Andrei Alexandrescu]

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