Rust Programming By Example

Pattern matching

So how can we know which variant is in a variable whose type is an enumeration and how to get the values out of it? For that, we need to use pattern matching. The match expression is one way to do pattern matching. Let's see how to use it to compute the result of an expression:

fn print_expr(expr: Expr) {
    match expr {
        Expr::Null => println!("No value"),
        Expr::Add(x, y) => println!("{}", x + y),
        Expr::Sub(x, y) => println!("{}", x - y),
        Expr::Mul(x, y) => println!("{}", x * y),
        Expr::Div { dividend: x, divisor: 0 } => println!("Divisor          is zero"),
        Expr::Div { dividend: x, divisor: y } => println!("{}",          x/y),
        Expr::Val(x) => println!("{}", x),
    }
}

A match expression is a way to check whether a value follows a certain pattern ...