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

1 files changed, 52 insertions, 0 deletions

diff --git a/src/common/error.h b/src/common/error.h
new file mode 100644
index 000000000..6fef3eb4b
--- /dev/null
+++ b/src/common/error.h
@@ -0,0 +1,52 @@
+// 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.
+#pragma once
+
+#include <system_error>
+#include <type_traits>
+
+enum class common_error : int
+{
+    // 0 is reserved for no error, as per expect<T>
+    kInvalidArgument = 1, //!< A function argument is invalid
+    kInvalidErrorCode     //!< Default `std::error_code` given to `expect<T>`
+};
+
+std::error_category const& common_category() noexcept;
+
+inline std::error_code make_error_code(::common_error value) noexcept
+{
+    return std::error_code{int(value), common_category()};
+}
+
+namespace std
+{
+    template<>
+    struct is_error_code_enum<::common_error>
+      : true_type
+    {};
+}