so what exactly is const supposed to mean?

[Hasan Aljudy]

Sean Kelly wrote:
> Hasan Aljudy wrote:
> 
>> Ok, I know that the const issue has apparently been beaten to death on 
>> the digitalmars.D NG, but ....
>>
>> Can someone please explain to me what does const mean?
> 
> 
> That depends.  Typically it means that a reference won't be used to 
> mutate referenced data, but that leaves a lot of room for 
> interpretation.  C++, for example, uses "logical const" for classes and 
> 'mutable' qualified members can actually be altered by const member 
> functions.  The mutable qualifier is useful in instances where a class 
> has members that are more of an implementation detail (a mutex or DB 
> connection handle, for example) that may need to be mutated in the 
> course of processing const-qualified methods.

hm, so basically making an object immutable?
Sorry, I didn't get the second part about C++. What do you mean by 
"logical const"?


>> I think it's something from C++, no? what is it? what does it do? and 
>> why do people think it's useful?
> 
> 
> Logical const (as in C++) provides a contract ensuring that the user of 
> const-qualified data will not modify it in observable ways.  This serves 
> to catch accidental errors and to make programmers feel better about 
> passing references into unknown code.

Is there anything preventing anyone from creating immutable classes?

> 
>> While you're at it, would you mind explaining the implications of 
>> implemeting the proposed "const by default" feature?
> [snip] 
> The implication is that references through which mutating operations 
> will occur would likely have to be qualified as 'mutable' or 'inout' or 
> some such, and that mutating member functions of classes and structs 
> would probably have to be labeled as 'mutable' as well.  But I don't 
> want to speculate beyond that as I haven't given the issue nearly as 
> much thought as Walter has.


damn, this doesn't sound too good.
I for one don't give a damn about const, so why should I be bothered to 
think about the constness of my code/classes and add "mutable" 
qualifiers all over the place?