Meaning of Leaky Abstraction?

Question

What does the term \"Leaky Abstraction\" mean? (Please explain with examples. I often have a hard time grokking a mere theory.)

Answer 1

It simply means that your abstraction exposes some of the implementation details, or that you need to be aware of the implementation details when using the abstraction. The term is attributed to Joel Spolsky, circa 2002. See the wikipedia article for more information.

A classic example are network libraries that allow you to treat remote files as local. The developer using this abstraction must be aware that network problems may cause this to fail in ways that local files do not. You then need to develop code to handle specifically errors outside the abstraction that the network library provides.