# Rustlings 测验 2：为什么 i 的类型是 &usize 而不是 usize

##### 问题描述投票：0回答：1

``````
// quiz2.rs
// This is a quiz for the following sections:
// - Strings
// - Vecs
// - Move semantics
// - Modules
// - Enums

// Let's build a little machine in the form of a function.
// As input, we're going to give a list of strings and commands. These commands
// determine what action is going to be applied to the string. It can either be:
// - Uppercase the string
// - Trim the string
// - Append "bar" to the string a specified amount of times
// The exact form of this will be:
// - The input is going to be a Vector of a 2-length tuple,
//   the first element is the string, the second one is the command.
// - The output element is going to be a Vector of strings.
// No hints this time!

// I AM NOT DONE

pub enum Command {
Uppercase,
Trim,
Append(usize),
}

mod my_module {
use super::Command;

// TODO: Complete the function signature!
pub fn transformer(input: Vec<(String, Command)>) -> Vec<String> {
// TODO: Complete the output declaration!
let mut output: Vec<String> = vec![];
for (string, command) in input.iter() {
// TODO: Complete the function body. You can do it!
let s = match command {
Command::Uppercase => string.to_uppercase(),
Command::Trim => string.trim().into(),
Command::Append(i: &usize) => format!("{}{}", string.to_owned(), "bar".repeat(*i))
};
output.push(s)
}
output
}
}

#[cfg(test)]
mod tests {
// TODO: What do we need to import to have `transformer` in scope?
use crate::my_module::transformer;
use super::Command;

#[test]
fn it_works() {
let output = transformer(vec![
("hello".into(), Command::Uppercase),
("foo".into(), Command::Append(1)),
("bar".into(), Command::Append(5)),
]);
assert_eq!(output[0], "HELLO");
assert_eq!(output[2], "foobar");
assert_eq!(output[3], "barbarbarbarbarbar");
}
}
``````

``transformer``

``i``

``Command::Append(i)``
``&usize``

``usize``
``Command``

``Append(usize)``

``````Command::Append(i: &usize) => format!("{}{}", string.to_owned(), "bar".repeat(*i))
``````

transformer函数中，命令变量 是对 Command 枚举值的引用，因此当您 对其进行模式匹配并匹配 Command::Append(i) 案例， 我将引用存储在 Append 变体中的 usize 值。

rust rust-rustlings
##### 1个回答
0

``````match &Foo(99) {
Foo(x) => {},
}
``````

``Foo``

``ref``

``````match *&Foo(99) {
Foo(ref x) => {},
}
``````

``Foo``

``x``

``Foo``

``````for (string, command) in input.iter() {/*..*/}
``````

``input.iter()``

``&(String, Command)``

``(string, command)``

``command``

``&Command``

``````match command {
//..
Command::Append(i) => {/*..*/}
}
``````

``````match *command {
//..
Command::Append(ref i) => {/*..*/}
}
``````

``i``

``&usize``