Logical const

[Peter Alexander]

On 29/11/10 11:13 PM, Walter Bright wrote:
> Peter Alexander wrote:
>> On 29/11/10 8:58 PM, Walter Bright wrote:
>>> Because people coming from C++ ask "why not do it like C++'s?"
>>
>> No one is asking this.
>
> I interpreted this from Jonathon as asking for it:
>
> "Without immutable, you could presumably get something similar
> to what C++ has (if you could ever get Walter to go for it),"
>
> You also wrote:
>
> "I can be sure that my object will come back unmodified. That it is the
> primary purpose of const. Like you said, it allows you to reason about
> your programs.
> Yes, GameObject could be unreasonably mutilated by careless use of
> mutable, but in practice that simply doesn't happen."
>
> Which implies that you regard C++'s system as sufficient. I pointed out
> 5 reasons why the "be sure" is incorrect. I believe it is necessary to
> discuss and understand these points in order to justify why D does not
> adopt C++'s system.

That was in response to your claim that C++'s const provides no 
guarantees. I was just giving a counterexample.

Just to clarify my position

- I *do not* want to copy C++'s const system.
- D style immutability is useful.
- C++ style logical const is also useful.
- I think they can both work side by side by introducing a new level of 
const and the mutable keyword.