Rust4.2 Common Collections

Rust学习笔记

Rust编程语言入门教程课程笔记

参考教材: The Rust Programming Language (by Steve Klabnik and Carol Nichols, with contributions from the Rust Community)

Lecture 8: Common Collections

fn main() {
    //Vector
    let mut v: Vec<i32> = Vec::new();//new empty vector
    v.push(1);
    let v2 = &v[0];//immutable borrow
    //v.push(2);//mutable borrow
    //cannot borrow `v` as mutable because it is also borrowed as immutable
    //because v.push will cause the vector to reallocate and invalidate the reference
    //so v2 may be pointing to deallocated memory
    println!("The first element is: {}", v2);

    let mut u = vec![1, 2, 3];//new vector with values
    println!("u[0] = {:?}", u[0]);//access element with index
    println!("u[1] = {:?}", u.get(1));//access element with get()

    match u.get(1) {
        Some(second) => println!("The second element is {}", second),
        None => println!("There is no second element."),
    }

    u.insert(0, 0);//insert element at index

    for i in &u {//immutable borrow
        println!("{}", i);
    }

    for i in &mut u {//mutable borrow
        *i += 50; //dereference i and add 50 to it
    }

    //using enum to store multiple types in a vector
    enum SpreadsheetCell {
        Int(i32),
        Float(f64),
        Text(String),
    }

    let row = vec![
        SpreadsheetCell::Int(3),
        SpreadsheetCell::Float(10.12),
        SpreadsheetCell::Text(String::from("blue")),
    ];

    for i in &row {//for + match
        match i {
            SpreadsheetCell::Int(i) => println!("Int: {}", i),
            SpreadsheetCell::Float(f) => println!("Float: {}", f),
            SpreadsheetCell::Text(s) => println!("Text: {}", s),
        }
    }

    //String
    let mut s = String::new();//new empty string
    println!("{}", s);
    let data = "initial contents 0";//new string from string literal
    s = data.to_string();//new string from string literal
    println!("{}", s);
    s = "initial contents 1".to_string();//new string from string literal
    println!("{}", s);
    s = String::from("initial contents 2");//new string from string literal
    println!("{}", s);

    s.push_str("bar");//append string literal
    println!("{}", s);

    s.push('l');//append char
    println!("{}", s);

    //concatenation
    let s1 = String::from("Hello, ");
    let s2 = String::from("world!");
    let s3 = s1 + &s2;//s1 has been moved here and can no longer be used
    println!("{}", s3);

    //format! macro
    let s1 = String::from("tic");
    let s2 = String::from("tac");
    let s3 = String::from("toe");
    let s4 = format!("{}-{}-{}", s1, s2, s3);//s1, s2, s3 not moved
    println!("{}", s1);
    println!("{}", s2);
    println!("{}", s3);
    println!("{}", s4);

    //indexing
    let s1 = String::from("hello");
    //let h = s1[0];//cannot index into a String
    let h = &s1[0..1];//indexing with range
    println!("{}", h);

    //length
    let len = String::from("Hola").len();//length in bytes
    println!("{}", len);
    let len = String::from("Здравствуйте").len();//length in bytes
    println!("{}", len);
    let len = String::from("Здравствуйте").chars().count();//length in chars
    println!("{}", len);

    //iteration
    for c in "नमस्ते".chars() {
        println!("{}", c);
    }

    for b in "नमस्ते".bytes() {
        println!("{}", b);
    }

    //Hash Map
    //HashMap stores a mapping of keys of type K to values of type V
    use std::collections::HashMap;//hashmap is not in the prelude

    let mut scores = HashMap::new();//new empty HashMap
    scores.insert(String::from("Blue"), 10);//insert key-value pair
    scores.insert(String::from("Yellow"), 50);//insert key-value pair
    println!("{:?}", scores);

    //collecting into a hashmap
    let teams = vec![String::from("Blue"), String::from("Yellow")];//new vector
    let initial_scores = vec![10, 50];//new vector
    let scores: HashMap<_, _> = teams.iter().zip(initial_scores.iter()).collect();//collect into hashmap
    //HashMap<_,_> type annotation is needed because collect can collect into many different data structures
    //zip() creates a vector of tuples
    println!("{:?}", scores);

    //ownership
    let field_name = String::from("Favorite color");
    let field_value = String::from("Blue");
    let mut map = HashMap::new();//new empty hashmap
    //map.insert(field_name, field_value);//field_name and field_value are moved into map
    //println!("{}", field_name);//field_name and field_value are moved into map
    map.insert(&field_name, &field_value);//field_name and field_value are borrowed
    println!("{}", field_name);//field_name and field_value are borrowed

    //accessing values in a hashmap
    let team_name = String::from("Blue");
    let score = scores.get(&team_name);//get() returns an Option<&V>
    
    match score {
        Some(s) => println!("{}", s),
        None => println!("No score"),
    }

    //iterating over a hashmap
    for (key, value) in &scores {
        println!("{}: {}", key, value);
    }

    //updating a hashmap

    //overwriting a value
    let mut scores = HashMap::new();//new empty hashmap
    scores.insert(String::from("Blue"), 10);//insert key-value pair
    scores.insert(String::from("Blue"), 25);//overwrite value
    println!("{:?}", scores);

    //only inserting a value if the key has no value
    scores.entry(String::from("Yellow"));//insert key-value pair if key has no value
    scores.entry(String::from("Yellow")).or_insert(50);//insert key-value pair if key has no value
    scores.entry(String::from("Blue")).or_insert(50);//do not insert key-value pair if key has value
    println!("{:?}", scores);

    //updating a value based on the old value
    let text = "hello world wonderful world";
    let mut map = HashMap::new();//new empty hashmap
    for word in text.split_whitespace() {//split string into words
        let count = map.entry(word).or_insert(0);//insert key-value pair if key has no value
        *count += 1;//dereference count and increment it
    }
    println!("{:?}", map);

}