Removing unnecessary template argument, but doesn't compile anymore

Question

I have two different approaches to a templated function using auto and decltype but one of them does not compile, yielding two error:

Where is the main difference between the following versions of the code:

This compiles

template<typename MemoryMapper, typename EngineParts>
class EngineBase {
    const MemoryMapper memoryMapper;
public:
    const EngineParts engineParts;
    EngineBase();
    virtual ~EngineBase();

    template<typename Mapper, typename MemoryAccessor>
    void getMemoryManager(void);

    template<MemoryMapper,typename MemoryAccessor>
    auto getMemoryManager(void)->decltype(memoryMapper.getMemoryManager<MemoryAccessor>())
    {
        return memoryMapper.getMemoryManager<MemoryAccessor>();
    }
};

While this does not

template<typename MemoryMapper, typename EngineParts>
class EngineBase {
    const MemoryMapper memoryMapper;
public:
    const EngineParts engineParts;
    EngineBase();
    virtual ~EngineBase();
    template<typename MemoryAccessor>
    auto getMemoryManager(void)->decltype(memoryMapper.getMemoryManager<MemoryAccessor>())
    {
        return memoryMapper.getMemoryManager<MemoryAccessor>();
    }
};

The error output is as follows:

g++ -O0 -g3 -Wall -c -fmessage-length=0 -std=c++0x -o EngineBase.o "..\\EngineBase.cpp" 
In file included from ..\EngineBase.cpp:7:0:
..\EngineBase.h:22:84: error: expected primary-expression before '>' token
  auto getMemoryManager(void)->decltype(memoryMapper.getMemoryManager<MemoryAccessor>())
                                                                                    ^
..\EngineBase.h:22:86: error: expected primary-expression before ')' token
  auto getMemoryManager(void)->decltype(memoryMapper.getMemoryManager<MemoryAccessor>())
                                                                                      ^

14:50:52 Build Finished (took 2s.587ms)

Since I don't want to specifically write the first template argument on every use and it would create the impression that there are more functions defined than realistically are, how can I get the second version to work without introducing another template argument? Function parameters would be ok, though.

Answer 1

template<typename MemoryAccessor>
auto getMemoryManager(void)->decltype(memoryMapper.template getMemoryManager<MemoryAccessor>())
//                                                 ~~~~~~~^
{
    return memoryMapper.template getMemoryManager<MemoryAccessor>();
    //                  ~~~~~~~^
}