Question

I’m trying to compile with g++ some code previously developed under Visual C++ 2008 Express Edition, and it looks like g++ won’t let me call a template method on a reference returned by a method of a template variable. I was able to narrow the problem down to the following code:

class Inner
{
public:
  template<typename T>
  T get() const
  {
    return static_cast<T>(value_);
  };
private:
  int value_;
};

class Outer
{
public:
  Inner const& get_inner() { return inner_; };
private:
  Inner inner_;
};

template<typename T>
int do_outer(T& val)
{
  return val.get_inner().get<int>();
}

int main()
{
  Outer outer;
  do_outer(outer);
  return 0;
}

The code compiles fine under Microsoft’s compiler, but g++ throws an error:

$ g++ -c main.cpp
main.cpp: In function ‘int do_outer(T&)’:
main.cpp:24: error: expected primary-expression before ‘int’
main.cpp:24: error: expected ‘;’ before ‘int’
main.cpp:24: error: expected unqualified-id before ‘>’ token

where line 24 refers to return val.get_inner().get<int>();.

If I make do_outer a normal method receiving an Outer reference the code compiles. Making Inner::get() a normal method also works. And making Inner::get() return void and receive a template parameter also works because the int specifier below becomes needless, i.e.:

class Inner
{
public:
  template<typename T>
  void get(T& val) const
  {
    val = static_cast<T>(value_);
  };
private:
  int value_;
};

...

template<typename T>
int do_outer(T& val)
{
  int i;
  val.get_inner().get(i);
  return i;
}

...

(g++ doesn’t complaing about the code above.)

Now I’m out of ideas. What’s the problem? Is there a problem with gcc/g++? Is there a compliance issue with my code?

The compiler I’m using is:

$ g++ --version
g++ (Ubuntu 4.3.3-5ubuntu4) 4.3.3

Answer 1

could you try with?

template<typename T>
int do_outer(T& val)
{
  return val.get_inner().template get<int>();
}

I don’t have access to gcc atm, but I’ve had similar issues and adding the template keyword always solved them. And it works in VS too.