new DIP5: Properties 2

[Andrei Alexandrescu]

Sergey Gromov wrote:
> Fri, 31 Jul 2009 21:37:06 -0500, Andrei Alexandrescu wrote:
> 
>> To clarify: if there was any extra checking by the compiler, any 
>> guarantee that the feature would provide at all, I'd be glad to pay the 
>> price of thinking more when putting together a design. But you want to 
>> define a language feature that allows people to require "()" or not as 
>> they please, and that's all. It's a frivolous detail to be spending time 
>> on when designing an API. I simply don't believe that's good language 
>> design.
> 
> That's not "all."  To me it's mostly maintainability.
> 
> If there is a property 'foo' and you allow to set it both as 'foo = 5'
> and 'foo(5)' then somebody *will* use the foo(5) form.  Making it hard,
> or even impossible for you, the maintainer, to switch from a property
> back to a regular field for 'foo'.
> 
> If you allow to call function 'bar()' both with and without parentheses,
> and a project is maintained by more than one person, they *will* call it
> differently making the source look inconsistent.
> 
> Dropping the 'omittable parentheses' thing happens to solve these, and
> the delegate return problem, and helps to disambiguate words with
> overloaded meanings.

Thanks for these great points. As an additional example, most ranges 
define the method

bool empty() { ... }

whereas infinite ranges define the enum

enum bool empty = false;

It follows that if a range user wants to be compatible with finite and 
infinite ranges, they always must use no "()". It would be nice if the 
range's definition could enforce that.


Andrei