Add return value header.

CMakeLists.txt

@@ -95,6 +95,7 @@ add_library(ViveLoaderLib STATIC
     GetComponent.h
     GetProvider.h
     InterfaceTraits.h
+    ReturnValue.h
     SearchPathExtender.h
     ServerDriverHost.cpp
     ServerDriverHost.h

ReturnValue.h

@@ -0,0 +1,110 @@
+/** @file
+    @brief Header
+
+    @date 2016
+
+    @author
+    Sensics, Inc.
+    <http://sensics.com/osvr>
+*/
+
+// Copyright 2016 Sensics, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//        http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef INCLUDED_ReturnValue_h_GUID_B28A8BE9_541A_42AC_6925_C51C944B089E
+#define INCLUDED_ReturnValue_h_GUID_B28A8BE9_541A_42AC_6925_C51C944B089E
+
+// Internal Includes
+// - none
+
+// Library/third-party includes
+// - none
+
+// Standard includes
+// - none
+
+namespace osvr {
+namespace vive {
+    struct ReturnValueBase {
+        ReturnValueBase() {}
+        ReturnValueBase(bool ok) : valid(ok) {}
+
+        const bool valid = false;
+
+        /// check validity by evaluating as a bool
+        explicit operator bool() const { return valid; }
+    };
+
+    template <typename ValueType, typename ErrorCodeType>
+    struct ReturnValue : ReturnValueBase {
+        ReturnValue(ValueType const &val, ErrorCodeType err)
+            : ReturnValueBase(), value(val), errorCode(err) {}
+        ReturnValue(ValueType const &val, ErrorCodeType err, bool ok)
+            : ReturnValueBase(ok), value(val), errorCode(err) {}
+
+        ValueType value = {};
+        ErrorCodeType errorCode = {};
+
+        static ReturnValue makeError(ErrorCodeType err) {
+            return ReturnValue{{}, err};
+        }
+        static ReturnValue makeValueFromRvalue(ValueType &&val) {
+            return ReturnValue{std::move(val), {}, true};
+        }
+        static ReturnValue makeValue(ValueType val) {
+            return ReturnValue{val, {}, true};
+        }
+    };
+
+    /// specialization for bool "error codes"
+    template <typename ValueType>
+    struct ReturnValue<ValueType, bool> : ReturnValueBase {
+        ReturnValue(ValueType const &val) : ReturnValueBase(true), value(val) {}
+        ReturnValue(ValueType const &val, bool ok)
+            : ReturnValueBase(ok), value(val) {}
+
+        ValueType value = {};
+
+        static ReturnValue makeError() { return ReturnValue{{}, false}; }
+        static ReturnValue makeValueFromRvalue(ValueType &&val) {
+            return ReturnValue{std::move(val), true};
+        }
+        static ReturnValue makeValue(ValueType val) {
+            return ReturnValue{val, true};
+        }
+    };
+
+    template <typename ValueType, typename ErrorCodeType>
+    inline ReturnValue<ValueType, ErrorCodeType>
+    makeGenericReturnValue(ValueType const &val, ErrorCodeType err,
+                           bool valid) {
+        using type = ReturnValue<ValueType, ErrorCodeType>;
+        return type(val, err, valid);
+    }
+
+    template <typename ValueType, typename ErrorCodeType>
+    inline ReturnValue<ValueType, ErrorCodeType> makeError(ValueType const &val,
+                                                           ErrorCodeType err) {
+        return makeGenericReturnValue(val, err, false);
+    }
+
+    template <typename ValueType, typename ErrorCodeType>
+    inline ReturnValue<ValueType, ErrorCodeType>
+    makeReturnValue(ValueType const &val, ErrorCodeType err) {
+        return makeGenericReturnValue(val, err, true);
+    }
+
+} // namespace vive
+} // namespace osvr
+#endif // INCLUDED_ReturnValue_h_GUID_B28A8BE9_541A_42AC_6925_C51C944B089E