@rocx If it's built in to the language and pervasively used, I'd consider Optional<T> to include the null value. However, optional types prevent the mistake, since the compiler checks ☺️
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Playing with optional type signatures in Python, I realise that the return type is the most important to me.
I'd much rather have a function with only a return type instead of a function with only parameter types. It's often quick to add too.
I'm never sure how to convert words with hyphens into SCREAMING_SNAKE_CASE. For example, should built-in function be BUILT_IN_FUNCTION or BUILTIN_FUNCTION?
Coming from JS or Python, imports in Rust feel weird. They're entirely optional aliases for fully qualified symbols, which are always available.
I don't know of many other languages where you can just start using libraries. Java is the only one I can think of.