Function calls

[Bill Baxter]

On Thu, Jan 28, 2010 at 3:58 PM, Nick Sabalausky <a at a.a> wrote:
> "Andrei Alexandrescu" <SeeWebsiteForEmail at erdani.org> wrote in message
> news:hjt449$5d8$1 at digitalmars.com...
>> Bill Baxter wrote:
>>> On Thu, Jan 28, 2010 at 2:27 PM, Andrei Alexandrescu
>>>>
>>>> The problem is not localized change. The result of stdin.byLine changes
>>>> the
>>>> _entire_ stdin.
>>>
>>> Ok, so you have no problem with a car.wheels returning a mutable wheels
>>> object?
>>> So it's only when the returned property can change the entire state
>>> (or a lot of the state?) that you have a problem?
>>> I don't understand how degree changes the acceptability.  Doesn't seem
>>> like it should matter to me.
>>
>> If you access car.wheel, it is reasonable to repaint that wheel. The
>> problem is that you can use car.wheel to repaint the car.
>>
>
> Ok, so you don't think a property of something should be able to change
> other parts of that something? Ok, I can understand that. But if that's so,
> then how would it be any better to be able to change something through the
> return value of one of that something's member functions? (Which, of course,
> is what stdin.byLine apperently already does.)
>
> Ie, Given this code:
>
> auto foo = stdin.byLine;
> foo.doSomethingThatAdvancesStdin();
>
> How is it possible for that code to be bad when "byLine" is defined as a
> "@property", but suddenly be perfectly fine when omittable parens are
> allowed and it's defined without "@property", even though either way it's
> still the exact same code doing exactly the same thing and having exactly
> the same effects?

That's not a contradiction in Andrei's position at all.  Because if
there is no @property, then all that dropping parens means is that
it's a no-function argument.  In the original D1 scheme,  .foo just
means foo is either field or a zero-arg function.  Nothing more
nothing less.  The problem is that you can't tell if the coder meant
it to be a property or not, and this bites you in cases like returning
callable.

--bb