SWIG: How to get value of wrapped std::shared_ptr from SwigPyobject

Question

I'm trying to create a SWIG Python interface for a C++ library, to add Python wrappers for some functions, and I would greatly appreciate some help from someone experienced with SWIG.

For now I have such sources:

test.h

namespace Test {
class CodeResponseEvent {
 public:
  CodeResponseEvent(std::string activation_code);
  std::string getActivationCode() const;
 private:
  const std::string activation_code_;
};

class CodeRequestEvent {
 public:
  CodeRequestEvent(std::string user_id);
  std::shared_ptr<CodeResponseEvent> execute();

 private:
  const std::string user_id_;
};
}

test.i

%module test
%include std_string.i
%include <std_shared_ptr.i>

%{#include "test.h"%}
%include "test.h"
%shared_ptr(Test::CodeResponseEvent);

Python code looks like:

codeResponse = test.CodeRequestEvent("user").execute()

As result I get value

<Swig Object of type 'std::shared_ptr< Test::CodeResponseEvent> *'>

So the question is how to unwrap this SwigPyobject to invoke getActivationCode() method?

Answer 1

You can just call the method on the object, but note you need to declare the %shared_ptr before %including the header. Here's a working standalone example. I've just %inlined the header for a one-file solution:

%module test
%include std_string.i
%include <std_shared_ptr.i>

%shared_ptr(Test::CodeResponseEvent);

%inline %{
#include <memory>
#include <string>
namespace Test {
class CodeResponseEvent {
 public:
  CodeResponseEvent(std::string activation_code) : activation_code_(activation_code) {}
  std::string getActivationCode() const { return activation_code_; }
 private:
  const std::string activation_code_;
};

class CodeRequestEvent {
 public:
  CodeRequestEvent(std::string user_id):user_id_(user_id) {};
  std::shared_ptr<CodeResponseEvent> execute() { return std::make_shared<CodeResponseEvent>("Hi"); }

 private:
  const std::string user_id_;
};
}
%}

Demo below. Note that r is a proxy instead of a generic Swig Object if the shared pointer is declared before use:

>>> import test
>>> r = test.CodeRequestEvent('user').execute()
>>> r
<test.CodeResponseEvent; proxy of <Swig Object of type 'std::shared_ptr< Test::CodeResponseEvent > *' at 0x0000027AF1F97330> >
>>> r.getActivationCode()
'Hi'