C++ temporary variables in initialization list

Question

In C++, is there any way to have something like a temporary variable in an initialization list. I want to initialize two constant members with the same instance of something

Answer 1

In C++11 you could use delegating constructors:

class Baz{
    const Foo f;
    const Bar b;
    Baz(Paramaters p) : Baz(p, temp(p)) { } // Delegates to a private constructor
                                            // that also accepts a Something
private:
    Baz(Paramaters p, Something const& temp): f(p,temp), b(p,temp) {
        // Whatever
    }
};

Answer 2

There's a couple of patterns to achieve this.

In C++11 use delegating constructors:

class Baz {
public:
    Baz(Paramaters p) :
        Baz{p, Something{p}}
    {}
private:
    Baz(Paramaters p, Something temp) :
        f{p, temp},
        b{p,temp}
    {}

    const Foo f;
    const Bar b;
};

Use a base class:

class BazBase {
public:
    BazBase(Paramaters p, Something temp) :
        f{p, temp},
        b{p,temp}
    {}
protected:
    const Foo f;
    const Bar b;
};

class Baz : private BazBase {
public:
    Baz(Paramaters p) :
        BazBase{p, Something{p}}
    {}
};

Use a factory method:

class Baz {
public:
    static Baz make(Parameters p)
    {
        return {p, Something{p}};
    }
private:
    Baz(Paramaters p, Something temp) :
        f{p, temp},
        b{p,temp}
    {}

    const Foo f;
    const Bar b;
};