[Swig-devel] [ swig-Bugs-2095124 ] [php5] Function returning object always returns new object

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Bugs item #2095124, was opened at 2008-09-05 15:39
Message generated for change (Comment added) made by olly
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Category: php
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Barry Cohen (barrycohen)
Assigned to: Olly Betts (olly)
Summary: [php5] Function returning object always returns new object

Initial Comment:
I've been working with SWIG for Python, Perl and PHP5 and have found the following to be a problem on PHP5 only.  Using SWIG 1.3.36.

Wrap the following C++ for php5:

== example.h ==

class Foo
{
  public:
    Foo() { i = 303; }
    int get_i() { return i; }

    Foo &update_i(Foo &f)
    {
      f.i *= 2;
      return f;
    }
  private:
    int i;
};

== example.i ==

%module example
%{
#include "example.h"
%}

%include "example.h"


The produced example.php then contains this update function:

class Foo {
  -- snip --
  function update_i($f) {
    $r=Foo_update_i($this->_cPtr,$f);
    return is_resource($r) ? new Foo($r) : $r;
  }
}


As far as I can tell, the whole is_resource() thing is used because the function is returning an object.  The problem is that $r is always a resource, so you always get a new Foo() back.  Consequently, this PHP:

$b = new Foo();
print $b->get_i() . "\n";
$b = $b->update_i($b);
print $b->get_i() . "\n";

produces

303
303

rather than

303
606

as you would hope.

This may seem like a bit of a contrived example, but the same thing happens if you create a C++ vector of structs, e.g.

== example.h ==

struct foo
{
  int bar;
};

== example.i ==

%module example
%rename(is_empty) empty;
%include "std_vector.i"

%{
#include "example.h"
%}

%template(v_foo) std::vector<foo>;

%include "example.h"


Again, the get() function in the v_foo class in example.php contains the is_resource() thing.  This leads to the following PHP error:


$v = new v_Foo();
$foo = new foo();
$foo->bar = 123;
$v->push($foo);
print $v->size() . "\n";
print $v->get(0)->bar . "\n";

This prints:

1
0

rather than

1
123

as you would expect, because a new foo() is returned from v_foo->get().

The biggest problem for me at the moment is that I can't think of a sensible workaround without modifying the way the initial C++ works.

Thanks

----------------------------------------------------------------------

>Comment By: Olly Betts (olly)
Date: 2009-07-29 12:09

Message:
Ah no, I was processing it without -c++, it does compile.

Sadly still broken, though the output for the first example is now:

303
0

Which I find harder to understand...

----------------------------------------------------------------------

Comment By: Olly Betts (olly)
Date: 2009-07-29 04:46

Message:
Hmm, well SVN trunk now generates C++ code which fails to compile for this
example.

I think this is fallout from the merge of vmiklos's PHP directors branch,
so I've asked him to take a look.

----------------------------------------------------------------------

Comment By: Olly Betts (olly)
Date: 2008-10-01 13:25

Message:
OK, so the issue seems to be that SWIG doesn't wrap an implicit copy ctor
unless you use %copyctor or -copyctor equivalent.

But the PHP backend isn't aware of this.


----------------------------------------------------------------------

Comment By: Olly Betts (olly)
Date: 2008-09-18 07:09

Message:
Creating the new PHP-side Foo object is OK as it's the wrapped C++ object
which matters (at least while we don't support directors for PHP).

Your example works if you explicitly define the copy constructor in
example.h:

    Foo(const Foo&o) : i(o.i) {}

Now I just need to figure out why...

----------------------------------------------------------------------

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