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Multiple inheritance has been a controversial issue for many years, [1] [2] with opponents pointing to its increased complexity and ambiguity in situations such as the "diamond problem", where it may be ambiguous as to which parent class a particular feature is inherited from if more than one parent class implements said feature.
Virtual inheritance is a C++ technique that ensures only one copy of a base class ' s member variables are inherited by grandchild derived classes. Without virtual inheritance, if two classes B and C inherit from a class A , and a class D inherits from both B and C , then D will contain two copies of A ' s member variables: one via B , and one ...
However, since multiple inheritance is slightly less efficient than single inheritance anyway, the overhead will not be a major problem. [ 1 ] [ 2 ] Cyclic reference - The Twin pattern relies on each twin referencing the other twin, which causes a cyclic reference scenario.
Virtual inheritance ensures that only one instance of a base class exists in the inheritance graph, avoiding some of the ambiguity problems of multiple inheritance. Multiple inheritance is a C++ feature allowing a class to be derived from more than one base class; this allows for more elaborate inheritance relationships. For example, a "Flying ...
For example, in a summary of C++ in his book on Objective C, Brad Cox actually claimed that adding multiple inheritance to C++ was impossible. Thus, multiple inheritance seemed more of a challenge. Since I had considered multiple inheritance as early as 1982 and found a simple and efficient implementation technique in 1984, I couldn't resist ...
The g++ compiler implements the multiple inheritance of the classes B1 and B2 in class D using two virtual method tables, one for each base class. (There are other ways to implement multiple inheritance, but this is the most common.) This leads to the necessity for "pointer fixups", also called thunks, when casting. Consider the following C++ code:
If used carelessly this feature can introduce some of the same system complexity and ambiguity classes were designed to avoid. [17] Most modern object-oriented languages such as Smalltalk and Java require single inheritance at run time. For these languages, multiple inheritance may be useful for modeling but not for an implementation.
C3 superclass linearization is an algorithm used primarily to obtain the order in which methods should be inherited in the presence of multiple inheritance.In other words, the output of C3 superclass linearization is a deterministic Method Resolution Order (MRO).