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;
> }
> 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
