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< h2 id = "destructuring" > < a class = "header" href = "#destructuring" > Destructuring< / a > < / h2 >
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< p > Let's look at some more destructuring. You can get the values from a struct or enum by using < code > let< / code > backwards. We learned that this is < code > destructuring< / code > , because you get variables that are not part of a structure. Now you have the values separately. First a simple example:< / p >
< pre > < pre class = "playground" > < code class = "language-rust" > 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);
}
< / code > < / pre > < / pre >
< p > This prints: < code > They call him Papa Doc but his real name is Clarence. He is 170 cm tall and is he happy? false< / code > < / p >
< p > You can see that it's backwards. First we say < code > let papa_doc = Person { fields }< / code > to create the struct. Then we say < code > let Person { fields } = papa_doc< / code > to destructure it.< / p >
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< p > You don't have to write < code > name: a< / code > - you can just write < code > name< / code > . But here we write < code > name: a< / code > because we want to use a variable with the name < code > a< / code > .< / p >
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< p > Now a bigger example. In this example we have a < code > City< / code > struct. We give it a < code > new< / code > function to make it. Then we have a < code > process_city_values< / code > function to do things with the values. In the function we just create a < code > Vec< / code > , but you can imagine that we can do much more after we destructure it.< / p >
< pre > < pre class = "playground" > < code class = "language-rust" > 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);
}
< / code > < / pre > < / pre >
< p > This prints < code > The city's two names are [" Tallinn" , " Reval" ]< / code > .< / p >
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