[Aldor-l] Compiling setup

[Gabriel Dos Reis]

"Christian Aistleitner" <tmgisi at gmx.at> writes:

| Hello,
| 
| On Sun, 13 Aug 2006 02:02:25 +0200, Gabriel Dos Reis
| <gdr at integrable-solutions.net> wrote:
| 
| > Ralf Hemmecke <ralf at hemmecke.de> writes:
| >
| > | > | local a:String == "abc";
| > | > | In the second it would be quite questionable.
| > | ... what the value of a is after assignment
| > |     a.3 := char "X";
| >
| > Stephen gave me an explanation and if I did understand correctly, that
| > assignment is also OK.
| 
| sadly enough, this seems to have been a private discussion and has not
| been posted to aldor-l -- Or did I miss it?

You're correct that it was a private message.  He just reminded me
that since a is defined as

    a : String == "abc";

therefore with type String, and a String is modifiable, the
modification 

  a.3 := char "X" 

is OK.

| > [...]
| >
| > | Just being curious... is there a legal C program that defines a
| > | constant array, and a pointer (or whatever) to on element of that
| > | array and then modifies that entry in-place?
| >
| > If I understand the question correctly, the answer is "no".
| 
| For those being not familiar with C or C++:
| These languages also provide a modifier const (just doing what its
| name  suggests), which Aldor (currently) lacks.

OK, let me expand a little bit on this.

First of all, K&R lacks "const" -- it was an invention for "C with
Classes" (the precursor of C++) that the ANSI C committee adopted
later, sadly with a slightly different semantics.  However, given

     char *a = "hqdfnoioffe";

you can't modify what a points to -- though you're free to modify the
pointer a.  Notice that no const is involved there.

The reason is that in C, therefore in C++, modifiability really is a 
*property of the object*, not just that of the expression used to
access the object.  However, you are right that C++ does enforce those
properties more often than C by lifting most of them directly into the
static semantics.  For example the string literal

   "hqdfnoioffe"

has type

   const char[12]

in C++. The proper way to write the above declaration in C++ is

     const char *a = "hqdfnoioffe";

However, the declaration

     char *a = "hqdfnoioffe";

is also accepted for C-compatibility reasons, but deprecated.  The
semantics however remains that you can't modify what a points to.

-- Gaby