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The extra bugs in a statically typed program go in the duplicated code that someone copied and changed the type names on because their type system wasn't flexib

The extra bugs in a statically typed program go in the duplicated code that someone copied and changed the type names on because their type system wasn't flexible enough to let different types share the same code. This means that 3 years later when someone fixed a bug in part of the code, the bug remained in the other copy because the person writing the fix didn't know about the copy. For a simple example, consider Arrow.jl vs the C++ implementation of the Arrow format. The Julia implementation is roughly 1/10th the lines of code (with more functionality), so even if there are 5x more bugs per line, the code still has fewer bugs. Static types definitely reduce bugs per line, but they can still increase bugs per functionality.

jolux 4y ago
But there are plenty of static type systems that let different types share the same code, the problem you describe only exists in nominal type systems (like C++) as far as I know. With structural types like in TypeScript or Go you can express this trivially. For that matter you can do this with subtype polymorphism in most cases. In Rust you can do it with trait objects as long as you control either the type or the trait. Probably there’s a way to do it in C++ too.