Extended Type Design.

[Andrei Alexandrescu (See Website For Email)]

Derek Parnell wrote:
> On Fri, 16 Mar 2007 14:05:17 -0700, Andrei Alexandrescu (See Website For
> Email) wrote:
> 
>> Dan wrote:
>>> Wow...
>>>
>>> I've never put this much thought into const/final stuff.  Ultimately, the program *cannot* prevent data in memory from being changed.  It can at best prevent you from accidentally changing it; hence final and const declarations mean "I don't want anyone to change these, can you raise an error if someone tries to within D?"
>>>
>>> Also, the problem breaks down to 'what am I declaring const?'.  If I declare:
>>>
>>> const int* x; // is it the pointer, or the int?
>>>
>>> This doesn't seem important until you get to:
>>>
>>> const int[int**][]* x; // now what is it?
>>>
>>> Ultimately, you have this problem going through each and every pointer, array and value.  You could theoretically write this:
>>>
>>> const int[int**][]*[char[]][3][17][3,17]* x;  and now what are you going to do?  declare it:
>>>
>>> final const final final const const final final final final final const?
>>> Even final const! super const! final! const! doesn't work, in fact I agree it makes it worse.
>>>
>>> Good luck getting readability with that.
>>>
>>> Ultimately, something else needs to be developed.
>>>
>>> Perhaps a character we can use in alongside each item on the type declaration, or we need to be able to hit the whole line in one blow..
>>>
>>> Just my penny.
>> I'm not sure what this is meant to convey.
> 
> It is trying to convey the difficultly in determining which
> 'final'/'const'/'super const' instance refers to which part of the
> declaration.
> 
> Given ...
> 
>    int[int**][]*[char[]][3][17][3,17]* x;
> 
> and I want to make the 'x' immutable and the 'char[]' immutable, how does
> one write the declaration? Where does one place the 'final'/'const'/'super
> const' and where do the parenthesis go?

final int[int**][]*[const char[]][3][17][3,17]* x;

Andrei