Ahhh.. Hmmmm. Even with the array as a private variable?
On Sat, 28 Oct 2017, 8:41 pm Fernando Santagata, <nando.santag...@gmail.com>
wrote:
> Hello Simon,
> Thank you for your reply.
>
> I would use an array if I hadn't the constraint that in a NativeCall class
> I can't use a Perl6 Array, just a CArray.
> Anyway I couldn't add a CArray to the class, because it would change its
> size and I need to pass the reference to that class to a C function.
>
> On Sat, Oct 28, 2017 at 1:58 PM, Simon Proctor <simon.proc...@gmail.com>
> wrote:
>
>> Here's my very naive way of doing it.
>>
>> class A does Positional {
>> has $.a0 is rw;
>> has $.a1 is rw;
>> has $.a2 is rw;
>> has $.a3 is rw;
>> has $.a4 is rw;
>> has $.a5 is rw;
>> has @!arr;
>>
>> method TWEAK {
>> @!arr[0] := $.a0;
>> @!arr[1] := $.a1;
>> @!arr[2] := $.a2
>> <https://maps.google.com/?q=2%5D+:%3D+$.a2&entry=gmail&source=g>;
>> @!arr[3] := $.a3
>> <https://maps.google.com/?q=3%5D+:%3D+$.a3&entry=gmail&source=g>;
>> @!arr[4] := $.a4;
>> @!arr[5] := $.a5
>> <https://maps.google.com/?q=5%5D+:%3D+$.a5&entry=gmail&source=g>;
>> }
>> multi method elems() { 6 }
>> multi method AT-POS( $index ) {
>> return @!arr[$index];
>> }
>> multi method ASSIGN-POS( $index, $new ) {
>> @!arr[$index] = $new;
>> }
>> }
>>
>> On Sat, 28 Oct 2017 at 09:45 Fernando Santagata <
>> nando.santag...@gmail.com> wrote:
>>
>>> Hello,
>>>
>>> I was trying to write a NativeCall interface to a C library, but I
>>> stumbled upon a problem (
>>> https://stackoverflow.com/questions/44266457/array-of-structs-as-an-attribute-of-a-perl-6-nativecall-struct
>>> ).
>>> The best way to solve that problem would be to add a new keyword to the
>>> NativeCall module, which I think is quite hard, so I'm trying a less fancy
>>> alternative.
>>>
>>> The problem itself looks like this: I have a class with a bunch of
>>> elements which I would like to access as an array (I can't use a Perl6
>>> Array in a NativeCall class).
>>>
>>> Reducing the problem to the bare bones, my class looks like
>>>
>>> Class A {
>>> has $.a0 is rw;
>>> has $.a1 is rw;
>>> has $.a2 is rw;
>>> has $.a3 is rw;
>>> has $.a4 is rw;
>>> }
>>>
>>> My first attempt was to use meta methods to access the attributes:
>>>
>>> class A does Positional {
>>> has $.a0 is rw;
>>> has $.a1 is rw;
>>> has $.a2 is rw;
>>> has $.a3 is rw;
>>> has $.a4 is rw;
>>> method AT-POS($index) is rw {
>>> my $a = A.^attributes(:local)[$index];
>>> $a.get_value(self);
>>> }
>>> }
>>>
>>> This works if I just need to read the values, but if I needed to write
>>> them I should use the set_value metamethod:
>>>
>>> $a.set_value(self, $value);
>>>
>>> The detail I miss is: how do I know whether the AT-POS method has been
>>> called to produce an rvalue or an lvalue?
>>>
>>> The second attempt was to use a Proxy object:
>>>
>>> class A does Positional {
>>> has $.a0 is rw;
>>> has $.a1 is rw;
>>> has $.a2 is rw;
>>> has $.a3 is rw;
>>> has $.a4 is rw;
>>> method AT-POS(::?CLASS:D: $index) is rw {
>>> my $a = A.^attributes(:local)[$index];
>>> Proxy.new(
>>> FETCH => method () { $a.get_value(self) },
>>> STORE => method ($value) { $a.set_value(self, $value) }
>>> );
>>> }
>>> }
>>>
>>> sub MAIN
>>> {
>>> my A $a .= new;
>>> $a.a0 = 0;
>>> $a.a1 = 1;
>>> say $a[0];
>>> say $a[1];
>>> say $a[2];
>>> $a[0] = 42;
>>> say $a[0];
>>> }
>>>
>>> But this program just hangs.
>>> When run in the debugger I get this:
>>>
>>> >>> LOADING Proxy.p6
>>> + Exception Thrown
>>> | Died
>>> + Proxy.p6 (25 - 29)
>>> | }
>>> |
>>> | sub MAIN
>>> | {
>>> | my A $a .= new;
>>>
>>> I'm clueless here.
>>> What am I doing wrong?
>>> Can anyone help?
>>>
>>> Thank you!
>>>
>>> --
>>> Fernando Santagata
>>>
>>
>
>
> --
> Fernando Santagata
>
