DeduplicatingFunctionWrapper.h

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// Copyright 2015 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_DeduplicatingFunctionWrapper_h_GUID_56CC2963_C33D_4FAA_34AB_4562516FE97B
#define INCLUDED_DeduplicatingFunctionWrapper_h_GUID_56CC2963_C33D_4FAA_34AB_4562516FE97B

// Internal Includes
// - none

// Library/third-party includes
// - none

// Standard includes
#include <functional>
#include <type_traits>
#include <stdexcept>

namespace osvr {
namespace common {
    template <typename ArgumentType, typename StorageType = void>
    class DeduplicatingFunctionWrapper {
      public:
        using argument_type = ArgumentType;

        using storage_type = typename std::conditional<
            std::is_same<StorageType, void>::value,
            typename std::remove_const<
                typename std::remove_reference<ArgumentType>::type>::type,
            StorageType>::type;

        typedef void return_type;

        typedef std::function<return_type(argument_type)> function_type;

        explicit DeduplicatingFunctionWrapper(function_type const &f)
            : m_func(f), m_beenCalled(false) {}

        DeduplicatingFunctionWrapper() : m_beenCalled(false) {}

        void setFunction(function_type const &f) { m_func = f; }

        return_type operator()(argument_type arg, ...) {
            if (!m_func) {
                throw std::logic_error("Must set the function in "
                                       "DeduplicatingFunctionWrapper before "
                                       "calling it!");
            }
            if (!m_beenCalled) {
                // First call - always pass through.
                m_beenCalled = true;
                return m_do(arg);
            }
            if (arg != m_last) {
                // Not first call, but argument has changed
                return m_do(arg);
            }
            return m_defaultReturn();
        }

      private:
        static return_type m_defaultReturn() { return return_type(); }

        return_type m_do(argument_type arg) {
            m_last = arg;
            return m_func(arg);
        }

        function_type m_func;

        bool m_beenCalled;

        storage_type m_last;
    };
} // namespace common
} // namespace osvr

#endif // INCLUDED_DeduplicatingFunctionWrapper_h_GUID_56CC2963_C33D_4FAA_34AB_4562516FE97B