8. Common Collections
Learning objectives
- Identify the 3 most common collection types in the Rust standard library
- Know where collections are stored in memory and why it’s important
- Be able to access elements of a collection and iterate over all elements
- Know where to find information about Rust’s collection types and when to use them
Intro
What is a ‘collection’?
Collections are data structures for storing multiple values.
What about arrays and tuples?
- Yes, arrays and tuples can hold multiple values
- But, they are stored on the
stackwhile collections are stored on theheap- array, tuple: fixed size, known at compile time
- collections: variable size, not known at compile time
Common collections
vector: collection of numbersstring: collection of charactershash map: collection of key-value pairs
Vectors
Creating vectors
Access elements
Access elements - ownership & borrowing
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Iteration
Vectors with multiple types
enum
Strings
What are Strings?
- Collection of bytes
- In Rust standard library
- Built around vectors
- UTF-8
String vs str
String
- standard library
- dynamic size
- vector
str
- built into the language
- fixed size
- slice of the vector
More info: Rust User’s forum – Stack Overflow
Creating Strings
Combining Strings
Access elements
Internal representation of Strings
- Wrapper around
Vec<u8> - Vector of bytes
- UTF-8
String slices
Iteration
.chars()
Hash maps
Creating hash maps
You can create a hash map with new and add values with .insert
Access elements
use std::collections::HashMap;
let mut scores = HashMap::new();
scores.insert(String::from("Red"), 10);
scores.insert(String::from("Blue"), 20);
let blue_team = String::from("Blue");
let blue_score = scores.get(&blue_team).copied().unwrap_or(0); // 20getreturns anOption<&V>copiedreturns anOption<i32>instead ofOption<&i32>unwrap_orreturns0if there is no entry for"Blue"
Iteration
use std::collections::HashMap;
let mut scores = HashMap::new();
scores.insert(String::from("Red"), 10);
scores.insert(String::from("Blue"), 20);
for (key, value) in &scores {
println!("{key}: {value}");
} // Red: 10, Blue: 20Order is arbitrary
Updating - overwrite
Updating - add if not present
Updating - modify existing value
Resources
8. Common Collections