add Chapter18

Chapter18/cib/libs/stdx/cx_set.hpp

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+#pragma once
+
+#include <stdx/compiler.hpp>
+#include <stdx/concepts.hpp>
+#include <stdx/cx_map.hpp>
+#include <stdx/iterator.hpp>
+
+#include <cstddef>
+
+namespace stdx {
+inline namespace v1 {
+template <typename Key, std::size_t N> class cx_set {
+    std::array<Key, N> storage{};
+    std::size_t current_size{};
+
+  public:
+    using key_type = Key;
+    using value_type = Key;
+    using size_type = std::size_t;
+    using reference = value_type &;
+    using const_reference = value_type const &;
+    using iterator = value_type *;
+    using const_iterator = value_type const *;
+
+    constexpr cx_set() = default;
+    template <typename... Ts,
+              // NOLINTNEXTLINE(modernize-use-constraints)
+              std::enable_if_t<((sizeof...(Ts) <= N) and ... and
+                                stdx::convertible_to<key_type, Ts>),
+                               int> = 0>
+    constexpr explicit cx_set(Ts const &...ts)
+        : storage{static_cast<value_type>(ts)...}, current_size{sizeof...(Ts)} {
+    }
+
+    [[nodiscard]] constexpr auto begin() LIFETIMEBOUND -> iterator {
+        return std::data(storage);
+    }
+    [[nodiscard]] constexpr auto begin() const LIFETIMEBOUND -> const_iterator {
+        return std::data(storage);
+    }
+    [[nodiscard]] constexpr auto
+    cbegin() const LIFETIMEBOUND -> const_iterator {
+        return std::data(storage);
+    }
+
+    [[nodiscard]] constexpr auto end() LIFETIMEBOUND -> iterator {
+        return begin() + current_size;
+    }
+    [[nodiscard]] constexpr auto end() const LIFETIMEBOUND -> const_iterator {
+        return begin() + current_size;
+    }
+    [[nodiscard]] constexpr auto cend() const LIFETIMEBOUND -> const_iterator {
+        return cbegin() + current_size;
+    }
+
+    [[nodiscard]] constexpr auto size() const -> size_type {
+        return current_size;
+    }
+    constexpr static std::integral_constant<size_type, N> capacity{};
+
+    [[nodiscard]] constexpr auto contains(key_type const &key) const -> bool {
+        for (auto const &k : *this) {
+            if (k == key) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    constexpr auto insert(key_type const &key) -> bool {
+        if (contains(key)) {
+            return false;
+        }
+        storage[current_size++] = key;
+        return true;
+    }
+    constexpr auto insert(key_type &&key) -> bool {
+        if (contains(key)) {
+            return false;
+        }
+        storage[current_size++] = std::move(key);
+        return true;
+    }
+
+    constexpr auto erase(key_type const &key) -> size_type {
+        for (auto &k : *this) {
+            if (k == key) {
+                k = storage[--current_size];
+                return 1u;
+            }
+        }
+        return 0u;
+    }
+
+    template <typename Set> constexpr auto merge(Set s) -> void {
+        for (auto const &entry : s) {
+            insert(entry);
+        }
+    }
+
+    [[nodiscard]] constexpr auto empty() const -> bool {
+        return current_size == 0u;
+    }
+
+    constexpr auto clear() -> void { current_size = 0; }
+
+    [[nodiscard]] constexpr auto pop_back() -> key_type {
+        return storage[--current_size];
+    }
+};
+
+template <typename T, typename... Ts>
+cx_set(T, Ts...) -> cx_set<T, 1 + sizeof...(Ts)>;
+
+template <typename T, std::size_t N>
+constexpr auto ct_capacity_v<cx_set<T, N>> = N;
+} // namespace v1
+} // namespace stdx