From 1bdfedf3c6dfed1b8f503696d44ea74e0db8c465 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C3=A9o=20Lam?= <leo@innovatetechnologi.es>
Date: Fri, 2 Mar 2018 23:27:29 +0100
Subject: [PATCH] Common: Add a Result class

This adds a lightweight, easy to use std::variant wrapper intended to
be used as a return type for functions that can return either a result
or an error code.
---
 Source/Core/Common/Common.vcxproj         |  1 +
 Source/Core/Common/Common.vcxproj.filters |  1 +
 Source/Core/Common/Result.h               | 30 +++++++++++++++++++++++
 3 files changed, 32 insertions(+)
 create mode 100644 Source/Core/Common/Result.h

diff --git a/Source/Core/Common/Common.vcxproj b/Source/Core/Common/Common.vcxproj
index a518b531f1..5b64898b7b 100644
--- a/Source/Core/Common/Common.vcxproj
+++ b/Source/Core/Common/Common.vcxproj
@@ -138,6 +138,7 @@
     <ClInclude Include="PcapFile.h" />
     <ClInclude Include="Profiler.h" />
     <ClInclude Include="QoSSession.h" />
+    <ClInclude Include="Result.h" />
     <ClInclude Include="ScopeGuard.h" />
     <ClInclude Include="SDCardUtil.h" />
     <ClInclude Include="Semaphore.h" />
diff --git a/Source/Core/Common/Common.vcxproj.filters b/Source/Core/Common/Common.vcxproj.filters
index 50ea0f619d..58b75ff30f 100644
--- a/Source/Core/Common/Common.vcxproj.filters
+++ b/Source/Core/Common/Common.vcxproj.filters
@@ -59,6 +59,7 @@
     <ClInclude Include="PcapFile.h" />
     <ClInclude Include="Profiler.h" />
     <ClInclude Include="QoSSession.h" />
+    <ClInclude Include="Result.h" />
     <ClInclude Include="ScopeGuard.h" />
     <ClInclude Include="SDCardUtil.h" />
     <ClInclude Include="SettingsHandler.h" />
diff --git a/Source/Core/Common/Result.h b/Source/Core/Common/Result.h
new file mode 100644
index 0000000000..2c4f47b3d7
--- /dev/null
+++ b/Source/Core/Common/Result.h
@@ -0,0 +1,30 @@
+// Copyright 2018 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <variant>
+
+namespace Common
+{
+template <typename ResultCode, typename T>
+class Result final
+{
+public:
+  Result(ResultCode code) : m_variant{code} {}
+  Result(const T& t) : m_variant{t} {}
+  Result(T&& t) : m_variant{std::move(t)} {}
+  explicit operator bool() const { return Succeeded(); }
+  bool Succeeded() const { return std::holds_alternative<T>(m_variant); }
+  // Must only be called when Succeeded() returns false.
+  ResultCode Error() const { return std::get<ResultCode>(m_variant); }
+  // Must only be called when Succeeded() returns true.
+  const T& operator*() const { return std::get<T>(m_variant); }
+  const T* operator->() const { return &std::get<T>(m_variant); }
+  T& operator*() { return std::get<T>(m_variant); }
+  T* operator->() { return &std::get<T>(m_variant); }
+private:
+  std::variant<ResultCode, T> m_variant;
+};
+}  // namespace Common