If you're designing a standard library for a language, you have to find a balance between the conceptual purity of types (including there the ease of proving/validating/testing their correctness), and adding convenience methods. Different language designers will decide where that balance lies in different ways, but you can't satisfy everyone (e.g. other people might ask for an interface with a different set of features), so you have to draw the line somewhere. Besides, this choice is not limiting - it's easy to add a helper function or a wrapper that does this, or extend the class.
↧