Enum switch (#168)

example/example_switch.cpp

@@ -0,0 +1,112 @@
+// Licensed under the MIT License <http://opensource.org/licenses/MIT>.
+// SPDX-License-Identifier: MIT
+// Copyright (c) 2019 - 2021 Daniil Goncharov <neargye@gmail.com>.
+//
+// Permission is hereby  granted, free of charge, to any  person obtaining a copy
+// of this software and associated  documentation files (the "Software"), to deal
+// in the Software  without restriction, including without  limitation the rights
+// to  use, copy,  modify, merge,  publish, distribute,  sublicense, and/or  sell
+// copies  of  the Software,  and  to  permit persons  to  whom  the Software  is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE  IS PROVIDED "AS  IS", WITHOUT WARRANTY  OF ANY KIND,  EXPRESS OR
+// IMPLIED,  INCLUDING BUT  NOT  LIMITED TO  THE  WARRANTIES OF  MERCHANTABILITY,
+// FITNESS FOR  A PARTICULAR PURPOSE AND  NONINFRINGEMENT. IN NO EVENT  SHALL THE
+// AUTHORS  OR COPYRIGHT  HOLDERS  BE  LIABLE FOR  ANY  CLAIM,  DAMAGES OR  OTHER
+// LIABILITY, WHETHER IN AN ACTION OF  CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE  OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#include <iostream>
+
+#include <magic_enum.hpp>
+
+enum class Color { RED, BLUE, GREEN };
+
+template <Color C>
+constexpr std::string_view DoWork() {
+  return "default";
+}
+
+template <>
+constexpr std::string_view DoWork<Color::GREEN>() {
+  return "override";
+}
+
+// helper type for the visitor pattern
+template<class... Ts> struct overloaded : Ts... { using Ts::operator()...; };
+template<class... Ts> overloaded(Ts...) -> overloaded<Ts...>;
+
+
+int main() {
+  Color c = Color::RED;
+
+  auto lambda = [] (auto value) {
+    std::cout << DoWork<value>() << std::endl;
+  };
+
+  magic_enum::enum_switch(lambda, c); // prints "default"
+
+  c = Color::GREEN;
+
+  magic_enum::enum_switch(lambda, c); // prints "override"
+
+
+  // with object, explicit enum type
+  auto switcher1 = overloaded {
+    [] (auto val) -> std::enable_if_t <(Color::BLUE == decltype(val){}())> {
+      std::cout << "Blue" << std::endl;
+    },
+    [] (std::integral_constant<Color, Color::RED>) {
+      std::cout << "Red" << std::endl;
+    }
+  };
+
+  magic_enum::enum_switch<Color>(switcher1, 2 /* GREEN */); // prints nothing
+  magic_enum::enum_switch<Color>(switcher1, 1 /* BLUE */); // prints "Blue"
+  magic_enum::enum_switch<Color>(switcher1, 0 /* RED */); // prints "Red"
+
+
+  // explicit result type
+  auto switcher2 = overloaded {
+    [] (std::integral_constant<Color, Color::GREEN>) {
+      return "called with green argument";
+    },
+    [] (Color other) { // default case
+      auto name = magic_enum::enum_name(other); // not empty
+      return "default: " + std::string{name.data(), name.size()};
+    }
+  };
+
+  std::cout << magic_enum::enum_switch<std::string>(switcher2, Color::GREEN) << std::endl; // prints "called with green argument"
+  std::cout << magic_enum::enum_switch<std::string>(switcher2, Color::RED) << std::endl; // prints "default: RED"
+
+  auto empty = magic_enum::enum_switch<std::string>(switcher2, static_cast<Color>(-3)); // returns an empty string
+  assert(empty.empty());
+
+
+  // result with default object
+  std::cout << magic_enum::enum_switch<Color, std::string>(switcher2, -3, "unrecognized") << std::endl; // prints "unrecognized"
+
+  auto switcher3 = overloaded {
+    [] (std::integral_constant<Color, Color::RED>) {
+      return "red result";
+    },
+    [] (std::integral_constant<Color, Color::BLUE>) {
+      return std::nullopt;
+    }
+  };
+
+  std::cout << std::boolalpha;
+  std::cout << magic_enum::enum_switch<Color>(switcher3, "GREEN", std::make_optional("cica")).value() << std::endl; // prints default: "cica"
+  std::cout << magic_enum::enum_switch<Color>(switcher3, "RED", std::make_optional("cica")).value() << std::endl; // prints: "red result"
+  std::cout << magic_enum::enum_switch<Color>(switcher3, "BLUE", std::make_optional("cica")).has_value() << std::endl; // prints: false
+  std::cout << magic_enum::enum_switch<Color>(switcher3, "red", std::make_optional("cica"), magic_enum::case_insensitive).value() << std::endl; // prints: "red result"
+
+  std::cout << magic_enum::enum_switch(switcher3, Color::GREEN, std::make_optional("cica")).value() << std::endl; // prints default: "cica"
+  std::cout << magic_enum::enum_switch(switcher3, Color::RED, std::make_optional("cica")).value() << std::endl; // prints: "red result"
+  std::cout << magic_enum::enum_switch(switcher3, Color::BLUE, std::make_optional("cica")).has_value() << std::endl; // prints: false
+}