【转】Options in Rust

原文：https://www.educative.io/edpresso/options-in-rust

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The Option enum in Rust can cater to two variants:

• None: represents a lack of value or if an error is encountered
• Some(value): value with type T wrapped in a tuple

Code

Let’s look at a case where the Option enum could come in handy. The work_experience function below uses a match operator to return either values or a None object based on a person’s occupation.

fn work_experience(occupation: &str) -> Option{
  match occupation{
    "Junior Developer" => Some(5),
    "Senior Developer" => Some(10),
    "Project Manager" => Some(15),
    _ => None
  }
}


fn main() {
  println!("Years of work experience for a junior developer: {}", match work_experience("Junior Developer"){
    Some(opt) => format!("{} years", opt),
    None => "0 years".to_string()
  });

  println!("\nYears of work experience for a student: {}", match work_experience("Student"){
    Some(opt) => format!("{} years", opt),
    None => "0 years".to_string()
  });
}