maybe_none.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) 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
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 *  a recipient may use your version of this file under either the CPAL or the GPL.
 *
 *  *** END LICENSE INFORMATION ***
 */
 
#pragma once
 
#include "../config/config.h"
 
namespace lass::python
{
 
/** Wrapper to type-hint return values in Python that maybe `None` but not likely.
 *
 *  Use this class to wrap a type T that could be None in Python (for example, a pointer type),
 *  but it is not likely to be None and forcing the user to expliclitly check for `None` can
 *  more painful than helpful. Annotating the type as `T | MaybeNone` instead of `T | None`
 *  will make static type-checkers like mypy ignore the `None` case, while still allowing
 *  the user to check for `None` if they want to. See [The Any Trick] for more information.
 *  
 *  @note This class does **NOT** prevent `None` values from being passed or returned,
 *  and it does **NOT** provide any runtime or compile-time checks whatsoever.
 *  It only alters the type-hint in Python for static type-checkers.
 *
 *  MaybeNone<T> types can only be returned from C++ to Python, it doesn't make sense to
 *  have them as function parameters in C++.
 * 
 *  Built-in support for MaybeNone is provided for raw pointers `T*`, util::SharedPtr<T>,
 *  `std::shared_ptr<T>`, and `std::optional<T>`.
 *  To support your own types, you must specialize PyExportTraits, see PyExportTraitsMaybeNone
 *  for more information.
 *
 *  [The Any Trick]: https://typing.python.org/en/latest/guides/writing_stubs.html#the-any-trick
 *
 *  @ingroup Python
 *  @sa PyExportTraitsMaybeNone
 *  @sa PyExportTraits<MaybeNone<T*>>
 *  @sa PyExportTraits<MaybeNone<util::SharedPtr<T,S,C>>>
 *  @sa PyExportTraits<MaybeNone<std::shared_ptr<T>>>
 *  @sa PyExportTraits<MaybeNone<std::optional<T>>>
 *  @sa NoNone
 */
template <typename T>
class MaybeNone
{
public:
    MaybeNone(const T& x = T()): value_(x) {}
    MaybeNone(std::nullptr_t): value_(nullptr) {}
 
    T& reference() { return value_; } ///< Return reference to wrapped value
    const T& reference() const { return value_; } ///< Return reference to wrapped value
 
    operator T&() { return value_; }
    operator const T&() const { return value_; }
    auto operator->() const { return value_.operator->(); }
    auto operator->() { return value_.operator->(); }
    auto& operator*() const { return value_.operator*(); }
    auto& operator*() { return value_.operator*(); }
 
    bool operator!() const { return !value_; }
    explicit operator bool() const { return static_cast<bool>(value_); }
 
#if __cpp_impl_three_way_comparison
    auto operator<=>(const MaybeNone& other) const = default;
#endif
 
private:
    T value_;
};
 
#if !__cpp_impl_three_way_comparison
 
template <typename T> bool operator==(const MaybeNone<T>& a, const MaybeNone<T>& b) { return a.reference() == b.reference(); }
template <typename T> bool operator!=(const MaybeNone<T>& a, const MaybeNone<T>& b) { return a.reference() != b.reference(); }
template <typename T> bool operator<(const MaybeNone<T>& a, const MaybeNone<T>& b) { return a.reference() < b.reference(); }
template <typename T> bool operator>(const MaybeNone<T>& a, const MaybeNone<T>& b) { return a.reference() > b.reference(); }
template <typename T> bool operator<=(const MaybeNone<T>& a, const MaybeNone<T>& b) { return a.reference() <= b.reference(); }
template <typename T> bool operator>=(const MaybeNone<T>& a, const MaybeNone<T>& b) { return a.reference() >= b.reference(); }
template <typename T> bool operator==(const MaybeNone<T>& a, std::nullptr_t b) { return a.reference() == b; }
template <typename T> bool operator!=(const MaybeNone<T>& a, std::nullptr_t b) { return a.reference() != b; }
template <typename T> bool operator==(std::nullptr_t a, const MaybeNone<T>& b) { return a == b.reference(); }
template <typename T> bool operator!=(std::nullptr_t a, const MaybeNone<T>& b) { return a != b.reference(); }
 
#endif
 
}