结构有可见性的一个额外的级别，它们的字段可以是公共或私有的(这是默认值)。这种可见只有当结构是从那里它被定义的模块外部访问重要的，它的目标是信息隐藏(封装)。
| mod my { |
| // A public struct with public fields |
| pub struct WhiteBox { |
| pub contents: T, |
| } |
| // A public struct with private fields |
| #[allow(dead_code)] |
| pub struct BlackBox { |
| contents: T, |
| } |
| impl BlackBox { |
| // A public constructor |
| pub fn new(contents: T) -> BlackBox { |
| BlackBox { |
| contents: contents, |
| } |
| } |
| } |
| } |
| fn main() { |
| // Public structs with public fields can be constructed as usual |
| let white_box = my::WhiteBox { contents: "public information" }; |
| // and their fields can be normally accessed |
| println!("The white box contains: {}", white_box.contents); |
| // but public structs with private fields can't be constructed |
| // Error! `BlackBox` has private fields |
| //let black_box = my::BlackBox { contents: "classified information" }; |
| // TODO ^ Try uncommenting this line |
| // However, structs with private fields can still be created using |
| // constructors |
| let _black_box = my::BlackBox::new("classified information"); |
| // The private fields of a struct can't be accessed |
| // Error! The `contents` field is private |
| //println!("The black box contains: {}", _black_box.contents); |
| // TODO ^ Try uncommenting this line |
| } |
