export_traits_function.h

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/** @file
 *  @author Bram de Greve (bram@cocamware.com)
 *  @author Tom De Muer (tom@cocamware.com)
 *
 *  *** BEGIN LICENSE INFORMATION ***
 *
 *  The contents of this file are subject to the Common Public Attribution License
 *  Version 1.0 (the "License"); you may not use this file except in compliance with
 *  the License. You may obtain a copy of the License at
 *  http://lass.sourceforge.net/cpal-license. The License is based on the
 *  Mozilla Public License Version 1.1 but Sections 14 and 15 have been added to cover
 *  use of software over a computer network and provide for limited attribution for
 *  the Original Developer. In addition, Exhibit A has been modified to be consistent
 *  with Exhibit B.
 *
 *  Software distributed under the License is distributed on an "AS IS" basis, WITHOUT
 *  WARRANTY OF ANY KIND, either express or implied. See the License for the specific
 *  language governing rights and limitations under the License.
 *
 *  The Original Code is LASS - Library of Assembled Shared Sources.
 *
 *  The Initial Developer of the Original Code is Bram de Greve and Tom De Muer.
 *  The Original Developer is the Initial Developer.
 *
 *  All portions of the code written by the Initial Developer are:
 *  Copyright (C) 2023-2025 the Initial Developer.
 *  All Rights Reserved.
 *
 *  Contributor(s):
 *
 *  Alternatively, the contents of this file may be used under the terms of the
 *  GNU General Public License Version 2 or later (the GPL), in which case the
 *  provisions of GPL are applicable instead of those above.  If you wish to allow use
 *  of your version of this file only under the terms of the GPL and not to allow
 *  others to use your version of this file under the CPAL, indicate your decision by
 *  deleting the provisions above and replace them with the notice and other
 *  provisions required by the GPL License. If you do not delete the provisions above,
 *  a recipient may use your version of this file under either the CPAL or the GPL.
 *
 *  *** END LICENSE INFORMATION ***
 */
 
#pragma once
 
#include "python_common.h"
#include "pyobject_plus.h"
#include "export_traits.h"
#include "pyobject_call.inl"
#include "_lass_module.h"
 
namespace lass::python
{
 
namespace impl
{
 
class FunctionImplBase
{
public:
    virtual ~FunctionImplBase() = default;
    virtual PyObject* call(PyObject* args) const = 0;
};
 
template <typename R, typename... Args>
class FunctionImpl: public FunctionImplBase
{
public:
    using TFunction = std::function<R(Args...)>;
 
    FunctionImpl(TFunction func) : func_(std::move(func)) {}
 
    PyObject* call(PyObject* args) const override
    {
        return impl::callFunction(args, func_);
    }
 
    TFunction function() const { return func_; }
private:
    TFunction func_;
};
 
class LASS_PYTHON_DLL Function: public PyObjectPlus
{
    PY_HEADER(PyObjectPlus)
public:
    using TPimpl = std::unique_ptr<FunctionImplBase>;
 
    Function(TPimpl pimpl);
 
    template <typename R, typename... Args>
    Function(std::function<R(Args...)> v):
        Function(TPimpl(new FunctionImpl<R, Args...>(std::move(v))))
    {
    }
 
    template <typename R, typename... Args>
    bool get(std::function<R(Args...)>& v)
    {
        if (auto p = dynamic_cast< FunctionImpl<R, Args...>* >(pimpl_.get()))
        {
            v = p->function();
            return true;
        }
        return false;
    }
 
    static PyObject* _tp_call(PyObject* self, PyObject* args, PyObject* kwargs);
private:
    std::unique_ptr<FunctionImplBase> pimpl_;
};
 
template <typename R, typename... Args>
class Callable
{
public:
    Callable(TPyObjPtr callable):
        callable_(std::move(callable))
    {
    }
 
    R operator()(typename util::CallTraits<Args>::TParam... args) const
    {
        LockGIL LASS_UNUSED(lock);
        LASS_ASSERT(callable_);
        const TPyObjPtr oArgs = makeTuple(args...);
        const TPyObjPtr result(PyObject_CallObject(callable_.get(), oArgs.get()));
        if (!result)
        {
            fetchAndThrowPythonException(LASS_PRETTY_FUNCTION);
        }
        typedef ArgumentTraits<R> TraitsR;
        typename TraitsR::TStorage temp;
        if (pyGetSimpleObject(result.get(), temp) != 0)
        {
            fetchAndThrowPythonException(LASS_PRETTY_FUNCTION);
        }
        return TraitsR::arg(temp);
    }
 
    TPyObjPtr callable() const { return callable_; }
private:
    TPyObjPtr callable_;
};
 
}
 
/** Bidirectional wrapper between Callable objects and std::function.
 *
 *  Accepts Callable objects and wraps them in a std::function without checking the
 *  parameter types or return type, allowing to call them from C++. The parameters
 *  and return type are only checked when the function is called, and an exception will
 *  be raised if the types do not match.
 *
 *  From C++ to Python, the std::function is converted to a Callable object, so that it
 *  can be called from Python. Again, the parameter types and return type will be
 *  checked when the function is called.
 *
 *  In both directions, unwrapping a previously wrapped function will be attempted.
 *  I.e. if the std::function passed to Python already wraps a Callable Python object,
 *  this will be unwrapped and the Callable object will be passed back to Python. In the
 *  other direction, if a Callable object that was passed to C++ already wraps a
 *  std::function, *and* this std::function matches the correct signature, then the
 *  std::function will be unwrapped and passed to C++. In other words, both directions
 *  will guarantee a perfect round trip if possible. In all other cases, the Callable
 *  or std::function will be wrapped in a new std::function or Callable object.
 * 
 *  @ingroup PyExportTraits
 */
template <typename R, typename... Args>
struct PyExportTraits< std::function<R(Args...)> >
{
    static constexpr const char* py_typing = "Callable[[Args...], R]";
 
    static PyObject* build(std::function<R(Args...)> v)
    {
        using TCallable = impl::Callable<R, Args...>;
        if (TCallable* p = v.template target<TCallable>())
        {
            PyObject* r = p->callable().get();
            Py_XINCREF(r);
            return r;
        }
        return new impl::Function(std::move(v));
    }
    static int get(PyObject* obj, std::function<R(Args...)>& v)
    {
        impl::initLassModule(); // ensure the module is initialized
        if (PyType_IsSubtype(obj->ob_type, impl::Function::_lassPyClassDef.type()))
        {
            if (static_cast<impl::Function*>(obj)->get(v))
            {
                return 0;
            }
        }
        if (!PyCallable_Check(obj))
        {
            PyErr_SetString(PyExc_TypeError, "Not callable");
            return 1;
        }
        using TCallable = impl::Callable<R, Args...>;
        v = TCallable(fromNakedToSharedPtrCast<PyObject>(obj));
        return 0;
    }
};
 
}