Suggestion: object const'ness

[Tom]

Derek Parnell escribió:
> .
>>
>> If you see a signature like this:
>>
>> void doSomething(in SomeObj obj1, inout SomeObj obj2);
>>
>> You'll instantly expect that function "doSomething" doesn't modify obj1
> 
> But it doesn't modify 'obj1'. Remembering that 'obj1' is the reference 
> to the object and not the object itself.

If you read just below you'll notice I was referring to obj1 as the 
object and not as it's reference.
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>>    and do possibly modify obj2 (the object and not it's reference). Why 
>> would you want (in the most of the cases) to make "in" the reference 
>> itself?
> 
> Don't know. Simplier I guess.

Exactly, no one knows why, it's simply useless. At present, in D is 
perfectly pointless (merely informative) to use 'in' with reference 
parameters, at least for the 99% of the cases.

>> Currently D 'in Obj p' "behaves as" the rarely-used 'Obj *const p' and 
>> not as the widely and common 'const Obj *p' of C++ ("behave as" 
>> because I use pointers instead of references to illustrate the 
>> underlying behavior and C++ references are always const).
>>
>> Const is another level of protection against unintended behavior (i.e. 
>> bugs). In C++, const *can* be circumvented but one has to be horribly 
>> explicit to do that. No way you would unintentionally do that.
> 
> So everyone repeat after me ... D is not C++, D is not C++, D is not 
> C++, ...  ;-)

I know that Derek. Just that *many* of the users that come to D, don't 
know if you realize it, comes from the C++ world. It's understandable, 
we like the features of C++ but hate the syntax (and other stuff) and we 
see D as a better C++. It's perfectly natural to try to achieve the same 
things in D that we've achieved in C++. Don't be afraid, I'd hate to see 
D become another C++ (and that's not gonna happen for sure).

For C++ users, 'in' parameters (for references) are 'const Obj &o', 
inout/out parameters are 'Obj &o'. When you see that on a signature you 
can be "sure" (there's always some reasonable trust in the middle) the 
function will not modify the object (you don't care about the object 
reference). In D in/out/inout are just a disappointment (for C++ users). 
I've dreamed to see that keywords used with the same meaning as what 
I've mentioned above.

> --Derek Parnell
> Melbourne, Australia