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267 | /*
This file is part of KDBindings.
SPDX-FileCopyrightText: 2021 Klarälvdalens Datakonsult AB, a KDAB Group company <info@kdab.com>
Author: Sean Harmer <sean.harmer@kdab.com>
SPDX-License-Identifier: MIT
Contact KDAB at <info@kdab.com> for commercial licensing options.
*/
#pragma once
#include <kdbindings/property_updater.h>
#include <kdbindings/signal.h>
#include <iostream>
#include <memory>
#include <type_traits>
namespace KDBindings {
namespace Private {
template<typename X, typename Y, typename = void>
struct are_equality_comparable : std::false_type {
};
template<typename X, typename Y>
struct are_equality_comparable<X, Y,
std::enable_if_t<
std::is_same<
std::decay_t<
decltype(std::equal_to<>{}(std::declval<X>(), std::declval<Y>()))>,
bool>::value>> : std::true_type {
};
template<typename X, typename Y>
constexpr bool are_equality_comparable_v = are_equality_comparable<X, Y>::value;
} // namespace Private
struct ReadOnlyProperty : std::runtime_error {
ReadOnlyProperty() = delete;
using std::runtime_error::runtime_error;
};
template<typename T>
struct equal_to {
auto operator()(const T &x, const T &y) const noexcept
-> std::enable_if_t<Private::are_equality_comparable_v<T, T>, bool>
{
return std::equal_to<>{}(x, y);
}
template<typename X, typename Y>
auto operator()(const X &, const Y &) const noexcept
-> std::enable_if_t<!Private::are_equality_comparable_v<X, Y>, bool>
{
return false;
}
};
// This forwrad declaration is required so that
// Property can declare PropertyNode as a friend
// class.
namespace Private {
template<typename PropertyType>
class PropertyNode;
}
template<typename T>
class Property
{
public:
typedef T valuetype;
Property() = default;
~Property()
{
m_destroyed.emit();
}
explicit Property(T value) noexcept(std::is_nothrow_move_constructible<T>::value)
: m_value{ std::move(value) }
{
}
Property(Property<T> const &other) = delete;
Property &operator=(Property<T> const &other) = delete;
Property(Property<T> &&other) noexcept(std::is_nothrow_move_constructible<T>::value)
: m_value(std::move(other.m_value))
, m_valueAboutToChange(std::move(other.m_valueAboutToChange))
, m_valueChanged(std::move(other.m_valueChanged))
, m_destroyed(std::move(other.m_destroyed))
, m_updater(std::move(other.m_updater))
{
// We do not move the m_moved signal yet so that objects interested in the moved-into
// property can recreate any connections they need.
// If we have an updater, let it know how to update our internal value
if (m_updater) {
using namespace std::placeholders;
m_updater->setUpdateFunction(
std::bind(&Property<T>::setHelper, this, _1));
}
// Emit the moved signals for the moved from and moved to properties
m_moved.emit(*this);
other.m_moved.emit(*this);
m_moved = std::move(other.m_moved);
}
Property &operator=(Property<T> &&other) noexcept(std::is_nothrow_move_assignable<T>::value)
{
// We do not move the m_moved signal yet so that objects interested in the moved-into
// property can recreate any connections they need.
m_value = std::move(other.m_value);
m_valueAboutToChange = std::move(other.m_valueAboutToChange);
m_valueChanged = std::move(other.m_valueChanged);
m_destroyed = std::move(other.m_destroyed);
m_updater = std::move(other.m_updater);
// If we have an updater, let it know how to update our internal value
if (m_updater) {
using namespace std::placeholders;
m_updater->setUpdateFunction(
std::bind(&Property<T>::setHelper, this, _1));
}
// Emit the moved signals for the moved from and moved to properties
m_moved.emit(*this);
other.m_moved.emit(*this);
m_moved = std::move(other.m_moved);
return *this;
}
template<typename UpdaterT>
explicit Property(std::unique_ptr<UpdaterT> &&updater)
{
*this = std::move(updater);
}
template<typename UpdaterT>
Property &operator=(std::unique_ptr<UpdaterT> &&updater)
{
m_updater = std::move(updater);
// Let the updater know how to update our internal value
using namespace std::placeholders;
m_updater->setUpdateFunction(
std::bind(&Property<T>::setHelper, this, _1));
// Now synchronise our value with whatever the updator has right now.
setHelper(m_updater->get());
return *this;
}
void reset()
{
m_updater.reset();
}
Signal<const T &, const T &> &valueAboutToChange() const { return m_valueAboutToChange; }
Signal<const T &> &valueChanged() const { return m_valueChanged; }
Signal<> &destroyed() const { return m_destroyed; }
void set(T value)
{
if (m_updater) {
throw ReadOnlyProperty{
"Cannot set value on a read-only property. This property likely holds the result of a binding expression."
};
}
setHelper(std::move(value));
}
T const &get() const
{
return m_value;
}
Property<T> &operator=(T const &rhs)
{
set(std::move(rhs));
return *this;
}
T const &operator()() const
{
return Property<T>::get();
}
private:
void setHelper(T value)
{
if (equal_to<T>{}(value, m_value))
return;
m_valueAboutToChange.emit(m_value, value);
m_value = std::move(value);
m_valueChanged.emit(m_value);
}
T m_value;
// the signals in a property are mutable, as a property
// being "const" should mean that it's value or binding does
// not change, not that nobody can listen to it anymore.
mutable Signal<const T &, const T &> m_valueAboutToChange;
mutable Signal<const T &> m_valueChanged; // By const ref so we can emit the signal for move-only types of T e.g. std::unique_ptr<int>
// The PropertyNode needs to be a friend class of the Property, as it needs
// access to the m_moved Signal.
// The decision to make this Signal private was made after the suggestion by
// @jm4R who reported issues with the move constructors noexcept guarantee.
// (https://github.com/KDAB/KDBindings/issues/24)
// Ideally we would like to figure out a way to remove the moved signal entirely
// at some point. However currently it is still needed for Property bindings to
// keep track of moved Properties.
template<typename PropertyType>
friend class Private::PropertyNode;
Signal<Property<T> &> m_moved;
mutable Signal<> m_destroyed;
std::unique_ptr<PropertyUpdater<T>> m_updater;
};
template<typename T>
std::ostream &operator<<(std::ostream &stream, Property<T> const &property)
{
stream << property.get();
return stream;
}
template<typename T>
std::istream &operator>>(std::istream &stream, Property<T> &prop)
{
T temp;
stream >> temp;
prop.set(std::move(temp));
return stream;
}
namespace Private {
template<typename T>
struct is_property_helper : std::false_type {
};
template<typename T>
struct is_property_helper<Property<T>> : std::true_type {
};
template<typename T>
struct is_property : is_property_helper<std::decay_t<T>> {
};
} // namespace Private
} // namespace KDBindings
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