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148 lines
2.7 KiB
Markdown
148 lines
2.7 KiB
Markdown
---
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date: 20200915
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id: 2eec2c96-e006-4a53-b5cc-fd39f466a6b7
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title: Rust Vectors
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---
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# Traits
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## std
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### convert
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- [TryInto](20201119171245-tryinto)
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# Description
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Vectors allow you to store more than one value in a single data
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structure that puts all the values next to each other in memory. Vectors
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can only store values of the same type. They are useful when you have a
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list of items, such as the lines of text in a file or the prices of
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items in a shopping cart.
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# Creating a New Vector
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``` rust
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fn main() {
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let v: Vec<i32> = Vec::new();
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}
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```
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## vec! macro
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Rust can often infer the type of value you want to store in the Vector.
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For convenience one can also use the [vec!
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macro](https://doc.rust-lang.org/std/macro.vec.html).
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``` rust
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fn main() {
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let v = vec![1, 2, 3];
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}
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```
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# Updating a Vector
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``` rust
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fn main() {
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let mut v = Vec::new();
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v.push(5);
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v.push(6);
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v.push(7);
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v.push(8);
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}
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```
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# Dropping a Vector
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Like other [structs](20200831193417-structs), vectors are freed when
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they go out of scope, along with the vector contents:
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``` rust
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fn main() {
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{
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let v = vec![1, 2, 3, 4];
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// do stuff with v
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} // <- v goes out of scope and is freed here
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}
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```
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# Read Vector elements
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There are two ways to reference a value stored in a vector:
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``` rust
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fn main() {
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let v = vec![1, 2, 3, 4, 5];
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let third: &i32 = &v[2];
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println!("The third element is {}", third);
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match v.get(2) {
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Some(third) => println!("The third element is {}", third),
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None => println!("There is no third element."),
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}
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}
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```
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Using
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[get](https://doc.rust-lang.org/std/vec/struct.Vec.html#method.get)
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together with
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[match](https://doc.rust-lang.org/rust-by-example/flow_control/match.html)
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seems preferable, as trying to get non existant elements with method \#1
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will cause an \`index out of bounds\` panic:
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``` rust
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fn main() {
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let v = vec![1, 2, 3, 4, 5];
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let does_not_exist = &v[100];
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let does_not_exist = v.get(100);
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}
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```
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When the `get` method is passed an index that is outside the vector, it
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returns `None` without panicking.
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# Iteration
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## Immutable references
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``` rust
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fn main() {
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let v = vec![100, 32, 57];
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for i in &v {
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println!("{}", i);
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}
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}
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```
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## Mutable references
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``` rust
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fn main() {
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let mut v = vec![100, 32, 57];
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for i in &mut v {
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*i += 50;
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}
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}
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```
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# Using Enums to store multiple types
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``` rust
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fn main() {
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enum SpreadsheetCell {
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Int(i32),
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Float(f64),
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Text(String),
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}
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let row = vec![
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SpreadsheetCell::Int(3),
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SpreadsheetCell::Text(String::from("blue")),
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SpreadsheetCell::Float(10.12),
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];
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}
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```
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