Is a square a rectangle? Liskov substitution principle in action

[giscus[bot]]

Is a square a rectangle? Liskov substitution principle in action

I will put that simple question in the room: "Is a square a rectangle?" And you might thank: "Well dah, of course!"
But wait for a second and let's check it together. We will use the L in SOLID: The Liskov Substitution principle to check if this relationship makes sense for us!

https://steven-giesel.com/blogPost/67425427-01cd-4707-8572-991c3f9c5fc2

[SmokeGlider]

Thank you for writing this example up. It looks good. However, on the Rectangle's Width and Height auto-implemented properties, I noticed you have the private access modifier on the set accessors. This won't work. They both should be protected. Otherwise, the derived class can't access them.
Also, and I think this is of more interest, if you replace 'override' with 'new' in the Square class methods, Liskov will be happy. A Square is a Square, and a Square is a Rectangle. And your unit test will pass once you correct the rectangle.SetHeigth typo.
Cheers!

[linkdotnet]

Hey, thanks for the comment.

I did fix the private/protected issue.

Also, and I think this is of more interest, if you replace 'override' with 'new' in the Square class methods, Liskov will be happy.

That is true and I never thought of this in that way. And you are right, it would fix the issue!

Much appreciated