Why there are no 'physical' object variables (only references)?

[Reiner Pope]

Kristian wrote:
> On Sun, 10 Sep 2006 18:59:34 +0300, Sean Kelly <sean at f4.ca> wrote:
>> Kristian wrote:
>>> And, I hope that D will have a 'const' type specifier in the future. 
>>> Now you cannot know if a function will modify an object that is 
>>> passed to it as a parameter. Or if a member function of a class will 
>>> change the internal status of the object.
>>
>> Don't we all.  But wanting it and coming up with a solid proposal for 
>> how it should work are entirely different issues, unfortunately.
> 
> Well, what's wrong with the way C++ does it?
> 
> class Obj {
>     void f() const;
>     void g();
> 
>     int v;
> }
> 
> void func(const Obj o) {
>     o.f();    //ok
>     o.g();    //error
>     o.v = 1;  //error
> }

Do some searching for 'const' and 'readonly' on this NG, and you should 
get the idea:
  - C++ const is ugly, so people don't use it enough;
  - const_cast removes the safety guarantees of const, making 
const-directed optimizations by the compiler impossible.
  - overloading by const requires duplication of code.
  - a trivial const system like C++ is too strict and may require 
unnecessary clones to avoid a static const violation, thus necessitating 
the need for const_cast
  - reference immutability (C++'s 'readonly view') is only one form of 
const, and can't guarantee other (important) immutability contracts
  - after such a problems, the merits are not so clear, since the 
usefulness can only really be attributed to two things:
     1. Standardising documentation of variable usage.
     2. Getting the compiler to help catch programmer errors.
   and some people claim that they have never found any bugs by using const.

Cheers,

Reiner