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Telegram/lib_base/base/optional.h

@@ -0,0 +1,57 @@
+// This file is part of Desktop App Toolkit,
+// a set of libraries for developing nice desktop applications.
+//
+// For license and copyright information please follow this link:
+// https://github.com/desktop-app/legal/blob/master/LEGAL
+//
+#pragma once
+
+#include <optional>
+
+namespace base {
+
+template <typename Type>
+struct optional_wrap_once {
+	using type = std::optional<Type>;
+};
+
+template <typename Type>
+struct optional_wrap_once<std::optional<Type>> {
+	using type = std::optional<Type>;
+};
+
+template <typename Type>
+using optional_wrap_once_t = typename optional_wrap_once<std::decay_t<Type>>::type;
+
+template <typename Type>
+struct optional_chain_result {
+	using type = optional_wrap_once_t<Type>;
+};
+
+template <>
+struct optional_chain_result<void> {
+	using type = bool;
+};
+
+template <typename Type>
+using optional_chain_result_t = typename optional_chain_result<Type>::type;
+
+template <typename Type>
+optional_wrap_once_t<Type> make_optional(Type &&value) {
+	return optional_wrap_once_t<Type> { std::forward<Type>(value) };
+}
+
+} // namespace base
+
+template <typename Type, typename Method>
+inline auto operator|(const std::optional<Type> &value, Method method)
+-> base::optional_chain_result_t<decltype(method(*value))> {
+	if constexpr (std::is_same_v<decltype(method(*value)), void>) {
+		return value ? (method(*value), true) : false;
+	} else {
+		return value
+			? base::optional_chain_result_t<decltype(method(*value))>(
+				method(*value))
+			: std::nullopt;
+	}
+}