if 表达式

if 表达式 的用法与其他语言中的 if 语句完全一样。

fn main() {
    let x = 10;
    if x == 0 {
        println!("zero!");
    } else if x < 100 {
        println!("biggish");
    } else {
        println!("huge");
    }
}

此外，你还可以将 if 用作一个表达式。每个块的最后一个表达式 将成为 if 表达式的值：

fn main() {
    let x = 10;
    let size = if x < 20 { "small" } else { "large" };
    println!("number size: {}", size);
}

Because if is an expression and must have a particular type, both of its branch blocks must have the same type. Show what happens if you add ; after "small" in the second example.

An if expression should be used in the same way as the other expressions. For example, when it is used in a let statement, the statement must be terminated with a ; as well. Remove the ; before println! to see the compiler error.