The double colon is used in place of the period for names based paths for calling functions or static methods on things. In a JavaScript world you're always using the period right no matter what to access anything sub sub module. So that's not necessarily how it works here. There are 13 different base types, including a ton of different integer types to different float types so we can talk extensively about all kinds of things. The Rust docs crates.io have this whole world that is kind of really encapsulated as being the way you do it rather than pick your package manager and testing library whatever.