struct graph

examples/types/CMakeLists.txt

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+cmake_minimum_required(VERSION 3.20)
+project(cex_type_demo LANGUAGES CXX)
+set(CMAKE_CXX_STANDARD 23)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+add_executable(type-demo main.cpp)

examples/types/main.cpp

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+#include "types.hpp"
+int main() { demo::Box<int> box(1); box.run(2); }

examples/types/meson.build

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+project('cex-type-demo', 'cpp', default_options: ['cpp_std=c++23'])
+executable('type-demo', 'main.cpp')

examples/types/types.hpp

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+#pragma once
+#include <concepts>
+#include <vector>
+namespace demo {
+template<class T> concept Addable = requires(T a) { a + a; };
+template<class T> concept Sized = requires(T a) { a.size(); };
+struct Base { int id; };
+struct Helper { int work() { return 1; } };
+template<Addable T>
+    requires std::copyable<T> && (Addable<T> || Sized<T>)
+struct Box : Base {
+    T value;
+    std::vector<T> entries;
+    Helper helper;
+    using value_type = T;
+    Box(Addable auto x) requires std::constructible_from<T, decltype(x)> : value(x) { helper.work(); }
+    template<Sized U> requires requires(U u) { u.size(); }
+    void set(const U& u) requires Addable<T> { helper.work(); }
+    void run(std::integral auto n) { helper.work(); }
+    template<class U> requires std::convertible_to<U, T>
+    void assign(U u) { value = u; }
+};
+using IntBox = Box<int>;
+enum class State { idle, ready };
+}