C9: std::String

Question 1

std::String

Answer 1

The String type, which is provided by Rust’s standard library rather than coded into the core language, is a growable, mutable, owned, UTF-8 encoded string type

Question 2

Creating a New String

Answer 2

let mut s = String::new();

Question 3

Using the to_string method to create a String from a string literal

Answer 3

let data = “initial contents”;

let s = data.to_string();

// the method also works on a literal directly:
let s = "initial contents".to_string();

Question 4

Using the String::from function to create a String from a string literal

Answer 4

let s = String::from(“initial contents”);

Question 5

Updating a String

Answer 5

let mut s1 = String::from(“foo”);
let s2 = “bar”;
s1.push_str(s2);
println!(“s2 is {s2}”);

Question 6

Concatenation with the + Operator

Answer 6

let s1 = String::from(“tic”);
let s2 = String::from(“tac”);
let s3 = String::from(“toe”);

let s = s1 + "-" + &s2 + "-" + &s3;

Question 7

Concatenation with the format! Macro

Answer 7

let s = format!(“{s1}-{s2}-{s3}”);

Question 8

Does this work?

let s1 = String::from("hello");
let h = s1[0];

Answer 8

NO:
$ cargo run
Compiling collections v0.1.0 (file:///projects/collections)
error[E0277]: the type String cannot be indexed by {integer}
–> src/main.rs:3:13
|
3 | let h = s1[0];
| ^^^^^ String cannot be indexed by {integer}
|
= help: the trait Index<{integer}> is not implemented for String
= help: the following other types implement trait Index<Idx>:
<String as Index<RangeFrom<usize>>>
<String as Index<RangeFull>>
<String as Index<RangeInclusive<usize>>>
<String as Index<RangeTo<usize>>>
<String as Index<RangeToInclusive<usize>>>
<String as Index<std::ops::Range<usize>>>
<str as Index<i>></i></usize></usize></usize></usize></RangeFull></usize>

For more information about this error, try rustc --explain E0277.
error: could not compile collections due to previous error

Question 9

Does this work?

let hello = “Здравствуйте”;
let answer = &hello[0];

Answer 9

NO

Question 10

Does this work?

let hello = “Здравствуйте”;

let s = &hello[0..4];

Answer 10

YES. Slicing Strings

Question 11

Methods for Iterating Over Strings

Answer 11

for c in “Зд”.chars() {
println!(“{c}”);
}

for b in “Зд”.bytes() {
println!(“{b}”);
}

Question 12

What is s?

let hello = “Здравствуйте”;

let s = &hello[0..4];

Answer 12

s = “Зд”

Here, s will be a &str that contains the first 4 bytes of the string. Earlier, we mentioned that each of these characters was 2 bytes, which means s will be Зд.