workspace, package, crate, module in rust

Module

Privacy

mod outer {
	mod a {
		pub mod aa {
		}
	}
	fn b(){}
}

a是b的sibling，b可以使用a中的pub item（functions, methods, structs, enums, modules, and constants）。a不需要加pub（a加pub含义是让module outer的同辈可以访问）；aa是b的child module，aa需要加pub才能让b访问。

能访问到module的名字，就能访问到module下的pub items（b能访问module名a，可以把module a想像成fn a，同一级当然可以访问；b能访问a后，就能访问a的pub item：module aa）

(the book 7.3)

Structs

Structs have an extra level of visibility with their fields. The visibility defaults to private, and can be overridden with the pub modifier. This visibility only matters when a struct is accessed from outside the module where it is defined, and has the goal of hiding information (encapsulation).
(rust by example 10.2)