Re^9: Small Perl 6 discoveries II, Rats

[syphilis]

That's a mutable "container" aka a variable (a Scalar in this case) containing one immutable value

I really do not understand the use of the term "immutable".
Is it perhaps meant to be some shorthand method of signifying that the numerator and denominator are co-prime ? (For this, the gmp C library documentation uses the term "canonical" - in the sense, I think, of "authoritative, standard, accepted".)
Admittedly, the connection between the meanings of "co-prime" and "immutable" seems very tenuous to me, but it's about all that I can come up with.

Cheers,
Rob

[raiph]

One thing's for sure -- you're confused! I apologize if the following still doesn't help and/or is aggravating.

I really do not understand the use of the term "immutable".

To me it means "never changes".

There are three exceptions:

Construction

A data item must go from uninitialized/undefined to initialized/defined:

my $foo := 42; # declares $foo at compile time, binds it to immutable 
+42 at run-time
BEGIN say $foo; # (Any)
$foo = 99; # Cannot assign to an immutable value

Destruction

Memory is of course reclaimed at the end of a process at the latest if not garbage collected earlier (when no more references to it exist).

Referencing mutable data

One can have a reference that is itself immutable but which refers to mutable data. (Rats aren't mutable. So please don't think "ah, maybe this is the issue". I'm just trying to be complete in elaborating on the precise meaning of "immutable" in P6.) Thus:

my @foo := (42, $);
@foo[1] = 99;
say @foo; # (42 99)
@foo[0] = 99; # Cannot modify an immutable Int

If your light bulb still hasn't lit up at least a little, perhaps it really is best for you to just wait until materials about P6 sufficiently improve (maybe years? maybe never?) and you have time to enjoy exploring them. (I don't think anyone can absorb new information well unless they're enjoying the process and it feels like you're very much not enjoying this at any level. I apologize if I've got that wrong.)

Alternatively, perhaps you could pick a line from my earlier comment in which I broke things down into tiny pieces, one that isn't clear to you, and we can then try to clear that up, and then another line, and so on?

[syphilis]

One thing's for sure -- you're confused!

Thanks - I think it was just a misunderstanding of what constitutes a "rational object".

I hope I'm correct in asserting that $x is a "rational object" if and only if $x.VAR.^name returns Rat - in which case it is impossible to assign to $x and the value that $x points to and returns cannot change (ie is immutable).
It seems somewhat similar to the perl5 scenario where one assigns $ref = \42;
In such a case the value of $$ref likewise cannot be altered (ie is immutable).

I'm further wondering if it's the case (in perl6) that $x is an immutable object whenever $x.var.^name returns anything other than Scalar ... though faik there could be other exceptions ...

Cheers,
Rob