1. The Diamond Problem
Its Solution
Copyright © 2017 Curt Hill

2. Multiple Inheritance Again
We see that in multiple inheritance we get all the properties and methods of two or more ancestral classes
This turns out to be a problem when multiple ancestors have the same property or method
The worst case of this is two derivations from the same hierarchy
Copyright © 2017 Curt Hill

3. Recall this Hierarchy person set_name employee student set_wage
set_major
grad
set_degree
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4. The Diamond Problem person set_name employee student set_wage
set_major
Student_worker
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5. The Issues
The Student Worker class now has two copies of name, birthdate and gender
It also has multiple copies of the methods
How is this solved?
In one sense this is a design problem
The wage part should come from elsewhere
Let’s ignore that and look at another way
Copyright © 2017 Curt Hill

6. Virtual Inheritance
In a recent version of C++ standards virtual inheritance was introduced for just this problem
This changes the student and employee classes
Student was: class student: | public person {
becomes: class student: | public virtual person {
Copyright © 2017 Curt Hill

7. Commentary We would also need a virtual after employee
However, student_worker would look like normal multiple inheritance
Copyright © 2017 Curt Hill

8. Implementation
If the student and employee do not use virtual inheritance then the student worker has two copies of the person
With virtual inheritance in student worker we only get one of these
We also get the extras from student and employee
Copyright © 2017 Curt Hill

9. Fix without need?
The diamond problem is largely used to show the problems of multiple inheritance
Virtual inheritance fixes this
As mentioned before is this example really a design problem?
Moreover, virtual inheritance does nothing about name clashes not caused by problems similar to the diamond problem
Copyright © 2017 Curt Hill