No, when you use a constructor you know you are dealing with the subtype. This allows you to have preconditions not required for the parent constructor such as other parameters. This is why in most languages the constructor name is that of the class being created. A good example of how this is that a … Read more
(This answer has been rewritten 2013-05-13, read the discussion in the bottom of the comments) LSP is about following the contract of the base class. You can for instance not throw new exceptions in the sub classes as the one using the base class would not expect that. Same goes for if the base class … Read more
LSP says that every subclass must obey the same contracts as the superclass. Wether or not this is the case for Collections.unmodifiableXXX() thus depends on how this contract reads. The objects returned by Collections.unmodifiableXXX() throw an exception if one tries to call any modifying method upon them. For instance, if add() is called, an UnsupportedOperationException … Read more
The answer depends on mutability. If your rectangle and square classes are immutable, then Square is really a subtype of Rectangle and it’s perfectly OK to derive first from second. Otherwise, Rectangle and Square could both expose an IRectangle with no mutators, but deriving one from the other is wrong since neither type is properly … Read more
Because an array allows fast access by index, and IList/IList<T> are the only collection interfaces that support this. So perhaps your real question is “Why is there no interface for constant collections with indexers?” And to that I have no answer. There are no readonly interfaces for collections either. And I’m missing those even more … Read more
Actually, I think I got the reason. I found an elegant way to add upcasting support to any trait that desires it, and that way the programmer is able to choose whether to add that additional vtable entry to the trait, or prefer not to, which is a similar trade-off as in C++’s virtual vs. … Read more
What is an example of the Liskov Substitution Principle?