Yes, the size of the object would change. In any case, I can't use a Perl6
Array in a NativeCall class, so the point is moot.
The problem is that that C library exposes an API, whose main structure
contains an array of five pointers to another kind of struct.
It is not a pointer to an array of pointers, but just an array of pointers.
So the struct contains an array of five pointers. (Does it sound weird? :-)
I really don't know why they designed that data container that way)
On Sat, Oct 28, 2017 at 9:47 PM, Simon Proctor <simon.proc...@gmail.com>
wrote:
> 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
>>
>
--
Fernando Santagata
