Revised RFC on range design for D2

[KennyTM~]

Simen Kjaeraas wrote:
> On Wed, 01 Oct 2008 07:58:20 +0200, Benji Smith 
> <dlanguage at benjismith.net> wrote:
> 
>> Bill Baxter wrote:
>>> On Tue, Sep 30, 2008 at 3:36 AM, Steven Schveighoffer
>>> <schveiguy at yahoo.com> wrote:
>>>>> There is no ambiguity either case. You evaluate Stdout.newline. The
>>>>> evaluation yields a value of some type. Then you evaluate formatln 
>>>>> against
>>>>> that value.
>>>> OK, then tell me what this does:
>>>>
>>>> x.y.z();
>>>>
>>>> Is y a property/field of x or a function call with no args?  I see a 
>>>> benefit
>>>> to being able to understand a line of code without requiring lots of 
>>>> extra
>>>> context.  I have to do less lookups of the source of a function or 
>>>> property.
>>>  The problem with this argument is that unless you disallow properties
>>> altogether, you still won't know whether y is actually a field or a
>>> call to a property method without looking it up.
>>>  --bb
>>
>> One thing that I've found especially annoying about the current 
>> implementation is this:
>>
>>    x.y = 3; // Working code
>>    x.y += 3; // Broken, if x.y is actually a function
>>    x.y = x.y + 3; // Ugly work-around
>>
>> I've been bitten by this at least a dozen different times. Having a 
>> real property syntax would eliminate cases like that.
>>
>> --benji
> 
> It seems we will soon get reference return values, in which case this would
> no longer be a problem. I have also written a property template that 
> enables
> things such as that, but it would also benefit immensely from reference
> return values.
> 

It's still an issue if we want to support property setters, say

   class Time {
     private double seconds;

     invariant /*pure?*/ double minutes () { return seconds/60.; }
     void minutes (invariant double x) { seconds = x*60.; }
   }

You cannot return a double& when calling .minutes because it simply does 
not exist. Therefore, the interpreter have to clever enough to convert

   t.minutes += 2;

into

   t.minutes = t.minutes + 2;

i.e.

   t.minutes(t.minutes() + 2);

if .minutes does not return a reference. A similar problem also exist 
with .opIndexAssign and .opSliceAssign.