运行时动态绑定和类继承之间的区别

Question

I am trying to clarify the concept of runtime dynamic binding and class inheritance in dynamic languages (Python, ruby) and static type languages (java, C++). I am not sure I am right or not.

In dynamic languages like Python and Ruby, runtime dynamic binding is implemented as duck typing. When the interpreter checks the type of an object, it checks whether the object has the specific method (or behaviour) rather than check the type of the object; and runtime dynamic binding does not mean class inheritence. Class inheritance just reduce code copy in Python and Ruby.

In static typed languages like Java and C++, runtime dynamic binding can be obtained only class inheritance. Class inheritance not only reduces code copy here, but is also used to implement runtime dynamic binding.

In summary, class inheritance and runtime dynamic binding are two difference concepts. In Python and Ruby, they are totally different; in Java and C++ they are mixed together.

Am I right?

Answer 1

You are correct in that runtime dynamic binding is entirely different conceptually from class inheritance.

But as I re-read your question, I don't think I would agree that "Java and C++, runtime dynamic binding is implemented as class inheritance." Class inheritance is simply the definition of broader behavior that includes existing behavior from existing classes. Further, runtime binding doesn't necessarily have anything to do with object orientation; it can refer merely to deferred method resolution.

Class inheritance refers to the "template" for how an object is built, with more and more refined behavior with successive subclasses. Runtime dynamic binding is merely a way of saying that a reference to a method (for example) is deferred until execution time. In a given language, a particular class may leverage runtime dynamic binding, but have inherited classes resolved at compile time.

In a nutshell, Inheritance refers to the definition or blueprint of an object. Runtime dynamic binding is, at its most basic level, merely a mechanism for resolving method calls at execution time.

EDIT I do need to clarify one point on this: Java implements dynamic binding on overridden class methods, while C++ determines a type through polymorphism at runtime, so it is not accurate for me to say that dynamic binding has "no relationship" to class inheritance. At a "macro" level, they're not inherently related, but a given language might leverage it in its inheritance mechanism.