[chuck-users] Cloning

[Stefan Blixt]

Yeah, the trouble with making your own clone method here is that members are
initialized once, and then written to again in the clone method. The cool
thing about constructors is that it offers a way to make a first
initialization of members depending on input to the constructor.

For a moment I thought you might be able to do something like this:

A cloneA;
class A {
        cloneA.x => int x;
        cloneA.y => int y;
}

1 => cloneA.x;
A a;
<<< "A.x=", a.x >>>;

... which is kind of insane (what would clone.x be before you assign the 1!)
Just for kicks I tried running it, rendering a "NullPointerException",
unsurprisingly.

/Stefan

On Fri, Dec 11, 2009 at 3:05 PM, Hans Aberg <haberg at math.su.se> wrote:

> ChucK does not have cloning for reference object, right? That is, the
> semantic equivalent of an this explicit copy-constructor pseudocode:
>  class A {...}
>  A a0;
>  ...
>  new A(a0) @=> A a1;
> That is, instead of merely setting a1 to the same reference as that of a0,
> create a new independent copy, and set its references to that of a0 (shallow
> copy).
>
> It is a problem in the program I wrote, scale.ck: if modifying tuning
> data, one actually manipulates the data of the original tuning loaded into
> memory. This is cool, but if I want to be able to reload the original data,
> I will have to write my own cloning operator.
>
> The difference is illustrated in the code below. First I make a shallow
> copy of a to b, which means that I can change b without changing a. Then I
> set a reference of a to b, after which changing b also changes a.
>
>  Hans
>
>
> ---- clone.ck ----
> class A {
>  string s;
> }
>
> A a; "a" @=> a.s;
> A b; "b" @=> b.s;
>
> chout <= "a.s = " <= a.s <= ", b.s = " <= b.s <= ".\n";
>
> "c" @=> b.s;
> chout <= "\"c\" @=> b.s; a = " <= a.s <= ", b = " <= b.s <= ".\n";
>
> a.s @=> b.s;
> chout <= "a.s @=> b.s; a.s = " <= a.s <= ", b.s = " <= b.s <= ".\n";
>
> "d" @=> b.s;
> chout <= "\"d\" @=> b.s; a.s = " <= a.s <= ", b.s = " <= b.s <= ".\n";
>
> a @=> b;
> chout <= "a @=> b; a.s = " <= a.s <= ", b.s = " <= b.s <= ".\n";
>
> "e" @=> b.s;
> chout <= "\"e\" @=> b.s; a.s = " <= a.s <= ", b.s = " <= b.s <= ".\n";
>
> ---- run ----
> $ chuck clone.ck
> a.s = a, b.s = b.
> "c" @=> b.s; a = a, b = c.
> a.s @=> b.s; a.s = a, b.s = a.
> "d" @=> b.s; a.s = a, b.s = d.
> a @=> b; a.s = a, b.s = a.
> "e" @=> b.s; a.s = e, b.s = e.
> --------
>
>
> _______________________________________________
> chuck-users mailing list
> chuck-users at lists.cs.princeton.edu
> https://lists.cs.princeton.edu/mailman/listinfo/chuck-users
>



-- 
Release me, insect, or I will destroy the Cosmos!
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.cs.princeton.edu/pipermail/chuck-users/attachments/20091211/91029d0a/attachment.html>