a more consistent const syntax

[Paul Collier]

Reiner Pope wrote:
> 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

Yeah, I guess there are a lot of tradeoffs with each syntax. I was 
wondering what the function pointers would look like as well...

const int function() p; // Current
const(this) int function() p; // Could be confusing in a member function
int const(function)() p; // Looks like a const function pointer
int function() const p; // C++ style

And combinations...

const(const const(int) function(const(int))) p;
const(const(this) const(int) function(const(int))) p;
const(const(int) const(function)(const(int))) p;
const(const(int) function(const(int)) const) p;

But the latter isn't really valid material for comparison. Anyways, I 
think the bikeshed should be orange! ;)