如何理解里式替换（LSP）？

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里式替换（LSP）的理解

Liskov Substitution Principle ——
If S is a subtype if T, then objects of type T may be replaced with objects of type S, without breaking the program. / Functions that use pointers of references to base classes must be able to use objects of derived classes without knowing it。

即子类对象能够替换程序中的父类对象出现的任何地方，并且保证原来程序的逻辑行为不变级正确性不被破坏。