CODEWITHSUNDEEP
c++inheritanceconstructor
Daniel Lee
Daniel Lee

Reputation: 2070

Construct object without arguments where superclass requires arguments

I'm implementing a class that inherits from a superclass. The superclass requires arguments for its constructor. I would like the subclass to be instantiatable without requiring arguments. The superclass looks like this:

class OtherClass {
public:
    OtherClass(YetAnotherClass *yac);
};
class SuperClass {
public:
    SuperClass(OtherClass *c);
};

I'd like to do something like this:

class MyClass : public SuperClass {
public:
  MyClass() : SuperClass(OtherClass(YetAnotherClass)) {}
};

In order to avoid having to do something like this when instantiating a member of MyClass:

YetAnotherClass * only_used_once = YetAnotherClass();
OtherClass * also_used_just_once = OtherClass(only_used_once);
MyClass what_i_actually_want = MyClass(also_used_just_once);

Is this possible? A similar question showed the solution of creating a static method that produces the arguments needed for the parent constructor, but I would hope there's a simpler way to get there.

Upvotes: 1

Views: 56

Answers (1)

Jarod42
Jarod42

Reputation: 217283

With :

struct DataClass
{
    DataClass() : yetAnotherClass(), otherClass(&yetAnotherClass) {}

    YetAnotherClass yetAnotherClass;
    OtherClass otherClass;
};

If each instance of MyClass owns the other class you may do the following:

class MyClass : private DataClass, public SuperClass
{
public:
  MyClass() : DataClass(), SuperClass(&this->otherClass) {}
};

else they share the other class and you may do:

class MyClass : public SuperClass
{
public:
    MyClass() : SuperClass(&dataClass.otherClass) {}
private:
    static DataClass dataClass;
};

DataClass MyClass::dataClass;

Upvotes: 1

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