Const Ideas

[Leandro Lucarella]

Adam D. Ruppe, el 30 de noviembre a las 13:38 me escribiste:
> int a;
> Adds an entry to the compiler's variable table named 'a' that references
> memory that is an int.
> 
> const(int) a;
> Add an entry named 'a' that references memory that is a constant int. The
> const() CTF takes the type int and returns a new type that is a constant int.
> 
> const int a;
> Add a *constant* entry named 'a' that references memory that is a mutable
> int.

But now you lost the idea of transitive constness (if your compile-time
pointer is const, the value it points to should be const). This doesn't
break your "model" if you think as if D works like Python, where int are
inmutables, but you can rebind the variable (your compile-time pointer).

Then:
const int a = 1;
means "I have a variable named 'a' that points to some int that has the
value 1 and I can't change where it points to (I can't rebind it)".

a = 2; is an error

const(int) b = 1;
means "I have a variable named 'b' that points to some int, conceptually
the same int as 'a', because there is no need to have more than 2
inmutable ints with the same value in the program, but I can change where
'b' points to (I can rebind it).".

so b = 2; is ok

So graphically:

     +---+
a -> | 1 | <- b
     +---+

and after b = 2;

     +---+         +---+
a -> | 1 |    b -> | 2 |
     +---+         +---+

Of course this is a "conceptual" model, otherwise there would not be value
passing and must be a reference internall, which I think is not that
efficient ;)

This is basically what happens with pointers and the values they point to.

-- 
Leandro Lucarella (luca) | Blog colectivo: http://www.mazziblog.com.ar/blog/
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