Adding expect<T> - a value-or-error implementation

1 files changed, 75 insertions, 0 deletions

diff --git a/src/common/error.cpp b/src/common/error.cpp
new file mode 100644
index 000000000..e091e4478
--- /dev/null
+++ b/src/common/error.cpp
@@ -0,0 +1,75 @@
+// Copyright (c) 2018, The Monero Project
+// All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#include "error.h"
+
+#include <string>
+
+namespace
+{
+    struct category final : std::error_category
+    {
+        virtual const char* name() const noexcept override final
+        {
+            return "common_category()";
+        }
+
+        virtual std::string message(int value) const override final
+        {
+            switch (common_error(value))
+            {
+                case common_error::kInvalidArgument:
+                    return make_error_code(std::errc::invalid_argument).message();
+                case common_error::kInvalidErrorCode:
+                    return "expect<T> was given an error value of zero";
+                default:
+                    break;
+            }
+            return "Unknown basic_category() value";
+        }
+
+        virtual std::error_condition default_error_condition(int value) const noexcept override final
+        {
+            // maps specific errors to generic `std::errc` cases.
+            switch (common_error(value))
+            {
+                case common_error::kInvalidArgument:
+                case common_error::kInvalidErrorCode:
+                    return std::errc::invalid_argument;
+                default:
+                    break;
+            }
+            return std::error_condition{value, *this};
+        }
+    };
+}
+
+std::error_category const& common_category() noexcept
+{
+    static const category instance{};
+    return instance;
+}
+