Initialize object in initializer list

Question

I have a class Foo where I need to initialize a reference to another class, but first I need to get some reference interfaces from another classes.

This is just a dummy code to explain a bit better my two questions:

class Foo
{
public:
  Foo();
  ~Foo();
private:
  int m_number;
  OtherClass& m_foo;
};

Foo::Foo() :
  m_number(10)
{
  // I really need to do this get's
  Class1& c1 = Singleton::getC1();
  Class2& c2 = c1.getC2();
  Class3& c3 = c2.getC3();

  //How can I put the m_foo initialization in the initialization list?
  m_foo(c3);
}

The questions are:

1 - I need to retrieve all those references above, before I initialize my member m_foo. But I would like to initialize the m_foo on the initialization list. What's the nicest way to accomplish that without having that in a single line. Is there any way?

2 - By doing the code above, I get the error:

error: uninitialized reference member 'OtherClass::m_foo' [-fpermissive]

Because I'm initializing with the parentheses as it would be done in the initialization list. How can I initialize then the m_foo properly?

@NathanOliver: I think the OP was pretty clear about this: Yes! "I really need to do this get's" — Waggili
– Waggili, Commented Sep 15, 2015 at 19:50
@Waggili Where? All he states is he needs them before he initializes m_foo — NathanOliver
– NathanOliver, Commented Sep 15, 2015 at 19:51
@waas1919 you're talking about member initializer lists not initializer_lists, I'd suggest modifying your title to make that clear. — mattnewport
– mattnewport, Commented Sep 15, 2015 at 19:57

Jarod42 · Accepted Answer · 2015-09-15 19:56:38Z

8

You may use delegating constructors (since C++11):

class Foo
{
public:
    Foo() : Foo(Singleton::getC1()) {}

private:

    explicit Foo(Class1& c1) : Foo(c1, c1.getC2()) {}
    Foo(Class1& c1, Class2& c2) : Foo(c1, c2, c2.getC3()) {}
    Foo(Class1& c1, Class2& c2, Class3& c3) : m_number(10), m_foo(c3)
    {
        // other stuff with C1, c2, c3
    }
    // ...
};

edited Sep 15, 2015 at 19:56

answered Sep 15, 2015 at 19:54

Jarod42

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