解构
我们再来看一些解构。你可以通过使用let
倒过来从一个结构体或枚举中获取值。我们了解到这是destructuring
,因为你得到的变量不是结构体的一部分。现在你分别得到了它们的值。首先是一个简单的例子。
struct Person { // make a simple struct for a person
name: String,
real_name: String,
height: u8,
happiness: bool
}
fn main() {
let papa_doc = Person { // create variable papa_doc
name: "Papa Doc".to_string(),
real_name: "Clarence".to_string(),
height: 170,
happiness: false
};
let Person { // destructure papa_doc
name: a,
real_name: b,
height: c,
happiness: d
} = papa_doc;
println!("They call him {} but his real name is {}. He is {} cm tall and is he happy? {}", a, b, c, d);
}
这个打印:They call him Papa Doc but his real name is Clarence. He is 170 cm tall and is he happy? false
你可以看到,这是倒过来的。首先我们说let papa_doc = Person { fields }
来创建结构。然后我们说 let Person { fields } = papa_doc
来解构它。
你不必写name: a
--你可以直接写name
。但这里我们写 name: a
是因为我们想使用一个名字为 a
的变量。
现在再举一个更大的例子。在这个例子中,我们有一个 City
结构。我们给它一个new
函数来创建它。然后我们有一个 process_city_values
函数来处理这些值。在函数中,我们只是创建了一个 Vec
,但你可以想象,我们可以在解构它之后做更多的事情。
struct City {
name: String,
name_before: String,
population: u32,
date_founded: u32,
}
impl City {
fn new(name: String, name_before: String, population: u32, date_founded: u32) -> Self {
Self {
name,
name_before,
population,
date_founded,
}
}
}
fn process_city_values(city: &City) {
let City {
name,
name_before,
population,
date_founded,
} = city;
// now we have the values to use separately
let two_names = vec![name, name_before];
println!("The city's two names are {:?}", two_names);
}
fn main() {
let tallinn = City::new("Tallinn".to_string(), "Reval".to_string(), 426_538, 1219);
process_city_values(&tallinn);
}
这将打印出The city's two names are ["Tallinn", "Reval"]
。