What is “Orthogonality”?

Question

What does \"orthogonality\" mean when talking about programming languages?

What are some examples of Orthogonality?

Answer 1

Most of the answers are very long-winded, and even obscure. The point is: if a tool is orthogonal, it can be added, replaced, or removed, in favor of better tools, without screwing everything else up.

It's the difference between a carpenter having a hammer and a saw, which can be used for hammering or sawing, or having some new-fangled hammer/saw combo, which is designed to saw wood, then hammer it together. Either will work for sawing and then hammering together, but if you get some task that requires sawing, but not hammering, then only the orthogonal tools will work. Likewise, if you need to screw instead of hammering, you won't need to throw away your saw, if it's orthogonal (not mixed up with) your hammer.

The classic example is unix command line tools: you have one tool for getting the contents of a disk (dd), another for filtering lines from the file (grep), another for writing those lines to a file (cat), etc. These can all be mixed and matched at will.