为什么不能在表达式中使用...语法？

Question

我正在尝试理解...语法。考虑以下程序：

fn how_many(x: i32) -> &'static str {
    match x {
        0 => "no oranges",
        1 => "an orange",
        2 | 3 => "two or three oranges",
        9...11 => "approximately 10 oranges",
        _ => "few oranges",
    }
}

fn pattern_matching() {
    for x in 0..13 {
        println!("{} : I have {} ", x, how_many(x));
    }
}

fn main() {
    // println!("{:?}", (2...6));
    pattern_matching();
}

在上面的程序中，模式匹配中使用的9...11编译正常。当我尝试在likeprintln!("{:?}", (2...6））中使用相同的代码时；我得到编译错误：

error: `...` syntax cannot be used in expressions
  --> src/main.rs:18:24
   |
18 |     println!("{:?}", (2...6));
   |                        ^^^
   |
   = help: Use `..` if you need an exclusive range (a < b)
   = help: or `..=` if you need an inclusive range (a <= b)

我试图理解为什么不能在println中使用。

Answer 1

因为同样的原因，你不能使用

太长别读：

• 每个人都不喜欢特定的语法

错误消息告诉您要使用的适当语法：

   = help: Use `..` if you need an exclusive range (a < b)
   = help: or `..=` if you need an inclusive range (a <= b)

fn how_many(x: i32) -> &'static str {
    match x {
        0 => "no oranges",
        1 => "an orange",
        2 | 3 => "two or three oranges",
        9..=11 => "approximately 10 oranges",
        _ => "few oranges",
    }
}

fn pattern_matching() {
    for x in 0..13 {
        println!("{} : I have {} ", x, how_many(x));
    }
}

fn main() {
    println!("{:?}", 2..=6);
    pattern_matching();
}