a more consistent const syntax

[Reiner Pope]

Paul Collier wrote:
> Rioshin an'Harthen wrote:
>> "Chris Nicholson-Sauls" <ibisbasenji at gmail.com> kirjoitti viestissä 
>> news:f951kq$2fss$1 at digitalmars.com...
>>> Daniel919 wrote:
>>>> 3. const P func(P p) { ... }
>>>> reads like: func returns a const(P)
>>>
>>> Which is, indeed, a problem -- in that I agree.
>>
>> I agree, as well. It reads like returning a const P.
>>
>>>> const / invariant alone (without brackets) is an attribute and has 
>>>> no other meaning
>>>> further proposal: returned types in a bracket at the end:
>>>> 3. const func (P p) (P) { ... }
>>>> //templated syntax: const func!(T) (T p) (T) { ... }
>>>
>>> Uhm.  Ew.  No, seriously, I just could not possibly handle that; I 
>>> would keep thinking I saw templates where there aren't any.  Worse 
>>> yet, for a long time I'll see the '!(' and keep wondering how I could 
>>> be instantiating a template in that position, when its really a 
>>> template declaration.  T'is a naughty naughty thing to mix the two -- 
>>> would give both the compiler and the user headaches.  IMHO, its the 
>>> 'const'/'invariant' keyword on methods that needs to move -- not sure 
>>> where it should go, though.  What looks best down here?  ;)  (First 
>>> listing is the current state, for reference.)
>>>
>>> const P       vunc       (P p)       { ... }
>>>       P const func       (P p)       { ... }
>>>       P const:func       (P p)       { ... }
>>>       P const(func)      (P p)       { ... }
>>>       P       func const (P p)       { ... }
>>>       P       func:const (P p)       { ... }
>>>       P       func       (P p) const { ... }
>>
>> Definitely the last one. It's immediately familiar to anyone with a 
>> C++ background, which I guess most of those coming to D has, and which 
>> I think are the people Walter is especially targetting. It also has 
>> the added bonus of not complicating method declaration grammar too much.
>>
>> Same list, this time a const func returning a const return value:
>>
>> const const(P) func (P p)
>> const(P) const func (P p)
>> const(P) const(func) (P p)
>> const(P) func const (P p)
>> const(P) func:const (P p)
>> const(P) func (P p) const
>>
>> I definitely prefer the last one as the cleanest of these.
> 
> Just chiming in on a slightly different note... the line that stuck out 
> in both examples for me was actually the const(func) line. That seems 
> really intuitive and consistent with the const syntax elsewhere.
> 
> I do find the const-on-the-end readable too, but really mostly because 
> of familiarity with C++ ;)

Although the idea is nice, I tried it out, and I don't like the look of it:

int const(getFoo)() { return foo; }

My main objection is that the const() is around getFoo, so you're saying 
that the function won't change -- but how can it, it's static data. What 
you really mean when you are saying it's a const function is that the 
this object is constant. So how about that?

const(this) int getFoo() { return foo; }

(It's syntactically unambiguous because this is a keyword)

  -- Reiner