163 lines
5.3 KiB
C++
163 lines
5.3 KiB
C++
#pragma once
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#include <tuple>
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#include <utility>
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// 少量样板代码的生成宏是可以接受的，
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// 等 concept 可以作为参数的那一天，这个宏就可以废弃了
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#define CREEPER_DEFINE_CHECKER(TRAIT) \
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struct checker final { \
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template <class T> \
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static constexpr bool result = TRAIT<T>; \
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};
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namespace creeper {
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/// CHECKER
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template <class T>
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concept checker_trait = requires {
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{ T::template result<void> };
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};
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template <checker_trait... Ts>
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struct CheckerOr {
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template <class T>
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static constexpr bool result = (Ts::template result<T> || ...);
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};
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template <checker_trait... Ts>
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struct CheckerAnd {
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template <class T>
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static constexpr bool result = (Ts::template result<T> && ...);
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};
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/// PROP
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template <class Token, typename T, auto interface>
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struct SetterProp : Token {
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T value;
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constexpr explicit SetterProp(T value) noexcept
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: value { std::move(value) } { }
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constexpr explicit operator T(this auto&& self) noexcept { return self.value; }
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template <typename O>
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auto operator=(O&& other) noexcept -> SetterProp&
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requires std::assignable_from<T&, O>
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{
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value = std::forward<O>(other);
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return *this; // x= y =6
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}
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auto apply(auto& self) const noexcept -> void
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requires requires { interface(self, std::declval<T>()); }
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{
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interface(self, value);
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}
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};
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template <class Token, typename T, auto interface>
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struct DerivedProp : T, Token {
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using T::T;
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template <typename... Args>
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requires std::constructible_from<T, Args&&...>
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constexpr explicit DerivedProp(Args&&... args)
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: T(std::forward<Args>(args)...) { }
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template <typename U>
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requires requires(T& t, U&& u) { t = std::forward<U>(u); }
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auto operator=(U&& value) -> DerivedProp& {
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T::operator=(std::forward<U>(value));
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return *this;
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}
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auto apply(this auto const& self, auto& widget) noexcept -> void {
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interface(widget, static_cast<const T&>(self));
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}
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};
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template <class Token, auto interface>
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struct ActionProp : Token {
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auto apply(auto& self) const noexcept -> void
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requires requires { interface(self); }
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{
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interface(self);
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}
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};
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/// @brief
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/// 声明式包装，非侵入式实现 Setter 的声明式化
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///
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/// 该包装器支持将 std::tuple 与单个 prop 混合传入，不受顺序限制。内部通过
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/// helper 检查 tuple 中的所有元素，递归调用 apply 将属性应用到 底层 Widget。
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/// 利用 CheckerT 延迟模板实例化，在 concept 层面约束属性类型， 从而避免因
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/// 递归参数展开而产生的海量且难以定位的模板错误。
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///
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/// @tparam W
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/// 需要被包装的组件类型。
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///
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/// @tparam checker
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/// 用于延迟模板实例化的“检查器”类型模板。典型形式如下：
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/// struct checker final {
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/// template <class T> struct result {
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/// static constexpr auto v = concept<T>;
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/// };
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/// };
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///
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/// @note
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/// 在不符合 checker 要求的类型被传入时，会在 concept 约束阶段直接报错，
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/// 提供简洁且精准的编译期错误提示，避免编译器自动展开大量构造函数
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/// 导致的冗长错误栈，但编译期报错信息依旧不友好。
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///
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template <class W, checker_trait checker>
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struct Declarative : public W {
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private:
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// For helpe check single props
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// 这里没法子塞一个 static_assert，无论如何这里都会被尝试错误地实例化
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template <typename T, class checker_>
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static constexpr auto impl_props_trait = checker_::template result<std::remove_cvref_t<T>>;
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// For help check tuple of props
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// 使用 SFINAE 真是抱歉，没找到方便处理 tuple 的方法真是不好意思呢
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template <typename T, class checker_>
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static constexpr auto impl_tuple_trait = false;
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template <typename... Ts, class checker_>
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static constexpr auto impl_tuple_trait<std::tuple<Ts...>, checker_> =
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(impl_props_trait<Ts, checker_> && ...);
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public:
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/* Export widget type */
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using Widget = W;
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/* Export checker type */
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using Checker = checker;
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/* For check props */
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template <class T>
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static constexpr auto props_trait = impl_props_trait<std::remove_cvref_t<T>, checker>;
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/* For check tuple */
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template <class T>
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static constexpr auto tuple_trait = impl_tuple_trait<std::remove_cvref_t<T>, checker>;
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public:
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// 铁血的，热血的，冷血的声明式构造接口
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explicit Declarative(auto&&... props) noexcept
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requires((props_trait<decltype(props)> || tuple_trait<decltype(props)>) && ...)
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: W {} {
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(apply(std::forward<decltype(props)>(props)), ...);
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}
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auto apply(auto&& tuple) noexcept -> void
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requires tuple_trait<decltype(tuple)>
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{
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std::apply([this](auto&&... args) { (apply(std::forward<decltype(args)>(args)), ...); },
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std::forward<decltype(tuple)>(tuple));
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}
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auto apply(auto&& prop) noexcept -> void
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requires props_trait<decltype(prop)>
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{
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std::forward<decltype(prop)>(prop).apply(*this);
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}
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};
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}
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