Question

I have to write 3 functions which accepts a parameter of BaseClass type and then return a DerivedClasses as the return value.

Public DerivedClass1 SimpleTest1(BaseClass baseType)
{
DerivedClass1 derivedClass1 = new DerivedClass1();
derivedClass1.item = baseType.item;
derivedClass1.itemGroup = baseType.itemGroup;
return derivedClass1;
}

Public DerivedClass2 SimpleTest2(BaseClass baseType)
{
DerivedClass2 derivedClass2 = new DerivedClass2();
derivedClass2.item = baseType.item;
derivedClass2.itemGroup = baseType.itemGroup;
return derivedClass2;
}

Public DerivedClass3 SimpleTest3(BaseClass baseType)
{
DerivedClass3 derivedClass3 = new DerivedClass3();
derivedClass3.item = baseType.item;
derivedClass3.itemGroup = baseType.itemGroup;
return derivedClass3;
}

The code written in all the 3 methods is the same! Is there a better way to achieve this, without code duplication? Is there a specific design pattern that I can apply here?

Answer 1

Use generics on this and you can express it fairly nicely:

public T SimpleTest<T>(BaseClass baseType) where T : BaseClass, new()
{
    T derived = new T();
    derived.item = baseType.item;
    derived.itemGroup = baseType.itemGroup;
    return derived;
}

There is one caveat that you have to have a default constructor or else this won’t work. In instances where you have a constructor with one or more arguments (but the same signature for each), you can dynamically instantiate the class using Reflection, as in dbaseman’s answer.