Hacker News Reader

About the square/rectangle example, what would be the solution? The Square subclass should not verify equality with width and height or it should not even exist? Or something else?

-- edit Wikipedia: If Square and Rectangle had only getter methods (i.e., they were immutable objects), then no violation of LSP could occur.

View on HN

> If Square and Rectangle had only getter methods (i.e., they were immutable objects), then no violation of LSP could occur.

Yeah, this is the fundamental problem; mutable objects tend to result in LSP violations when class heirarchies follow common sense is-a relationships, but mutating operations are not limited to those (if any exist) that preserve identity.

A corollary to this is that the use of default constructors very often accompanies LSP violations, as it usually implies all of the object's state is subject to mutating operations.

Reply on news.ycombinator.com