alt Hacker News> My favorite definition of “legacy code” is “code that is not tested” because no matter who writes code, it turns into a minefield quickly if it doesn’t have tests.
On the contrary, legacy code has, by definition, been battle tested in production. I would amend the definition slightly to:
“Legacy code is code that is difficult to change.”
Lacking tests is one common reason why this could be, but not the only possible reason.
It’s from Working Effectively with Legacy Code. I don’t recall the exact definition but it’s something to that effect. Legacy = lack of automated tests.
The biggest barrier to changing code is usually insufficient automated testing. People are terrified of changing code when they can’t verify the results before breaking production.
More glibly legacy code is “any code I don’t want to deal with”. I’ve seen code written 1 year prior officially declared “legacy” because new coding standards were being put in place and no one wanted to update the old code to match.