Why Static Typing Matters

After having worked with a 20-30k LOC Python project a few years ago I became a big believer in the power of static typing.

Lawrence Kesteloot articulated why static typing matters really well in his article:

For a few quick examples, think about what happens in a language that lacks static type annotations if you want to rename a method. You need to find all the call sites to that method. If you miss one, you’ve introduced a bug that won’t be found until it actually breaks a test case, is caught in QA, or makes it out to the field. In a language with static type annotations, you simply recompile, and the compiler will tell you where you missed (or, in most Java IDEs, you’ll get a real-time report of the remaining places you haven’t fixed, or better still, you use the IDE’s automated refactoring command to rename all the references to the method as well as its declaration, all rigorously correctly due to the type annotations). You may think this is a trivial matter, but it’s not. To find these cases yourself, you have to search the source tree. You’d better not miss any files (what about generated files, or files that someone else is working on, and checks in after your rename, still referring to the old name).