rust语言基础pub关键字及Some语法示例

// 模块定义
mod foo {
    // 函数定义，没有标记 pub
    fn private_function() {
        println!("This is a private function.");
    }
    // 函数定义，标记 pub
    pub fn public_function() {
        println!("This is a public function.");
    }
    // 结构体定义，标记 pub
    pub struct PublicStruct {
        pub field1: i32,
        field2: i32,
    }
    // 枚举定义，标记 pub
    pub enum PublicEnum {
        Option1,
        Option2,
    }
}
// 在另一个模块中使用 foo 模块中的公共函数和结构体
fn main() {
    foo::public_function(); // 可以调用公共函数
    let my_struct = foo::PublicStruct { field1: 42, field2: 13 }; // 可以创建公共结构体的实例
    // 编译错误：private_function 是私有函数，不能被访问
    // foo::private_function();
}

// An output can have either Some value or no value/ None.
enum Option<T> { // T is a generic and it can contain any type of value.
  Some(T),
  None,
}
// A result can represent either success/ Ok or failure/ Err.
enum Result<T, E> { // T and E are generics. T can contain any type of value, E can be any error.
  Ok(T),
  Err(E),
}

fn get_an_optional_value() -> Option<&str> {
    //if the optional value is not empty
    return Some("Some value");
    //else
    None
}

struct Name {
  first_name: String,
  middle_name: Option<String>, // middle_name can be empty
  last_name: String,
}