Strings
String
can be mutated.&str
borrowed, immutable string slice.References:
strings1.rs
// TODO: Fix the compiler error without changing the function signature.
fn current_favorite_color() -> String {
String::from("blue")
}
fn main() {
let answer = current_favorite_color();
println!("My current favorite color is {answer}");
}
In this exercise the function is expecting
String
as return type but got&str
instead."hello"
is&str
and we just need to convert it intoString
.We can use either one of below expressions:
String::from("blue") "blue".to_string()
strings2.rs
// TODO: Fix the compiler error in the `main` function without changing this function.
fn is_a_color_word(attempt: &str) -> bool {
attempt == "green" || attempt == "blue" || attempt == "red"
}
fn main() {
let word = String::from("green"); // Don't change this line.
if is_a_color_word(&word) {
println!("That is a color word I know!");
} else {
println!("That is not a color word I know.");
}
}
Similar problem with previous exercise.
The function is expecting
&str
but gotString
instead.So we can convert it using either codes below:
is_a_color_word(&word) is_a_color_word(word.as_str())
strings3.rs
fn trim_me(input: &str) -> &str {
// TODO: Remove whitespace from both ends of a string.
input.trim()
}
fn compose_me(input: &str) -> String {
// TODO: Add " world!" to the string! There are multiple ways to do this.
format!("{input} world!")
}
fn replace_me(input: &str) -> String {
// TODO: Replace "cars" in the string with "balloons".
input.replace("cars", "balloons")
}
fn main() {
// You can optionally experiment here.
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn trim_a_string() {
assert_eq!(trim_me("Hello! "), "Hello!");
assert_eq!(trim_me(" What's up!"), "What's up!");
assert_eq!(trim_me(" Hola! "), "Hola!");
}
#[test]
fn compose_a_string() {
assert_eq!(compose_me("Hello"), "Hello world!");
assert_eq!(compose_me("Goodbye"), "Goodbye world!");
}
#[test]
fn replace_a_string() {
assert_eq!(
replace_me("I think cars are cool"),
"I think balloons are cool",
);
assert_eq!(
replace_me("I love to look at cars"),
"I love to look at balloons",
);
}
}
In this exercise we have 3 task.
First is to trim given
&str
in functiontrim_me
and return&str
.We can use
trim
method to do this.
Second is to add
" world!"
into given&str
in functioncompose_me
.We have multiple option to do this.
But because
&str
is immutable we cannot just simply use+
.We can either convert it into
String
first or useformat
macro like below.format!("{input} world!") input.to_string() + " world!"
Last is to replace occurrence of
cars
toballoons
in functionreplace_me
.We can do this by using
replace
method.
strings4.rs
// Calls of this function should be replaced with calls of `string_slice` or `string`.
fn placeholder() {}
fn string_slice(arg: &str) {
println!("{arg}");
}
fn string(arg: String) {
println!("{arg}");
}
// TODO: Here are a bunch of values - some are `String`, some are `&str`.
// Your task is to replace `placeholder(…)` with either `string_slice(…)`
// or `string(…)` depending on what you think each value is.
fn main() {
string_slice("blue");
string("red".to_string());
string(String::from("hi"));
string("rust is fun!".to_owned());
string("nice weather".into());
string(format!("Interpolation {}", "Station"));
// WARNING: This is byte indexing, not character indexing.
// Character indexing can be done using `s.chars().nth(INDEX)`.
string_slice(&String::from("abc")[0..1]);
string_slice(" hello there ".trim());
string("Happy Monday!".replace("Mon", "Tues"));
string("mY sHiFt KeY iS sTiCkY".to_lowercase());
}
In this exercise we need to replace
placeholder
with eitherstring
orstring_slice
for given parameters.I explain each of the line below:
// "blue" is &str string_slice("blue"); // to_string() return String string("red".to_string()); // String string(String::from("hi")); // to_owned() return String string("rust is fun!".to_owned()); // Here, both answers work. // `.into()` converts a type into an expected type. // If it is called where `String` is expected, it will convert `&str` to `String`. string("nice weather".into()); // format return String string(format!("Interpolation {}", "Station")); // &str because it a slice string_slice(&String::from("abc")[0..1]); // trim return &str string_slice(" hello there ".trim()); // replace return String string("Happy Monday!".replace("Mon", "Tues")); // to_lowercase() return String string("mY sHiFt KeY iS sTiCkY".to_lowercase());
Basically anything that require string manipulation usually return
String
and if no string manipulation usually return&str
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