enum

6 Enum

Enums allow you to define a type by enumerating its possible variants.

6.1 define and use

enum IpAddrKind {
	V4,
	V6,
}
let four = IpAddrKind::V4;

rust中的enum可以接收不通类型的参数

enum IpAddr {
  V4(u8, u8, u8, u8),
  V6(String),
}

6.2 Option Enum

Rust does not have nulls, but it does have an enum that can encode the concept of a value being present or absent.
This enum is Option.

6.3 match

let some_u8_value = 0u8;
match some_u8_value {
	1 => println!("one"),
	3 => println!("three"),
	5 => println!("five"),
	7 => println!("seven"),
	_ => (),
}

• However, the match expression can be a bit wordy in a situation in which we care about only one of the cases.
• For this situation, Rust provides if let.

6.4 if let

if we only care about one of the case, we can use "if let"
let some_u8_value = Some(0u8);
match some_u8_value {
	Some(3) => println!("three"),
	_ => (),
}
等价于
if let Some(3) = some_u8_value {
	println!("three");
}