run-time-polymorphism | 易学教程

Using enums for dynamic polymorphism in Rust

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问题 When one already knows all the finite number of types involved in some code which needs dynamic polymorphism, using enum can be better for performances compared to using Box since the latter uses dynamic memory allocation and you'll need to use trait objects which have virtual function call as well. That said, compared to the equivalent code in C++ using std::variant and std::visit , looks like Rust in this scenario has more boilerplate coding involved, at least for me (I have not yet learned

Using enums for dynamic polymorphism in Rust

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Using enums for dynamic polymorphism in Rust

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Elaboration: Method overloading is a static/compile-time binding but not polymorphism. Is it correct to correlate static binding with polymorphism?

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问题 Before I ask my question, let me to explain my understanding and opinion. By only Overriding we can't achieve polymorphism unless there is upcasting. And as it can only seen at runtime people might have named it as Run time ploymorphism. ( I have no objection to call polymorphism as Run Time Polymorphism ) I have objection to call method overloading as compile time polymorphism or polymorphism . I agree that method overloading is static binding (compile time binding), but I can't see

Elaboration: Method overloading is a static/compile-time binding but not polymorphism. Is it correct to correlate static binding with polymorphism?

阅读更多关于 Elaboration: Method overloading is a static/compile-time binding but not polymorphism. Is it correct to correlate static binding with polymorphism?

Before I ask my question, let me to explain my understanding and opinion. By only Overriding we can't achieve polymorphism unless there is upcasting. And as it can only seen at runtime people might have named it as Run time ploymorphism. ( I have no objection to call polymorphism as Run Time Polymorphism ) I have objection to call method overloading as compile time polymorphism or polymorphism . I agree that method overloading is static binding (compile time binding), but I can't see polymorphism in that. According to the javadoc, there is only polymorphism . There is no compile time or run

Why can't I assign a parent class to a variable of subclass type?

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Why reference variable of child class can't point to object of parent? i.e Child obj = new Parent(); However we can do vice versa Kindly answer with memory view (heap) There is no reason which has something to do with the memory. It's much more simple. A subclass can extend the behaviour of its superclass by adding new methods. While it is not given, that a superclass has all the methods of its subclasses. Take the following example: public class Parent { public void parentMethod() {} } public class Child extends Parent { public void childMethod() {} } Now let's think about what would happen

Why can't I assign a parent class to a variable of subclass type?

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问题 Why reference variable of child class can't point to object of parent? i.e Child obj = new Parent(); However we can do vice versa Kindly answer with memory view (heap) 回答1: There is no reason which has something to do with the memory. It's much more simple. A subclass can extend the behaviour of its superclass by adding new methods. While it is not given, that a superclass has all the methods of its subclasses. Take the following example: public class Parent { public void parentMethod() {} }