In this blog post, we're going to see how to work with Options in Rust
Options
Since Rust doesn't support Nulls instead it has Optional value. Option is an Enum type which has 2 variants such as Some
and None
Use cases
Following are some of the use cases with Option in Rust
Variable Initiation
Function return values
Return values for otherwise reporting simple errors
Optional struct fields
Optional functional arguments
Variable Initiation
// Declaring variable with None
let a: Option<i32> = None;
// Declaring variable with Some(100)
let b: Option<i32> = Some(100);
Extracting Values from Option
Extracting values from Option can be done using various ways
if-let statement
if let Some(x) = a {
println!("Value of variable a => {x}");
}
match expression
match b {
Some(x) => println!("Value of variable b => {x}"),
None => println!("Value of variable b => None"),
}
expect method
expect
method panics with a provided custom message when the variable is of None
variant
println!("Value of variable a => {}", b.expect("Variable cannot be empty"));
unwrap method
unwrap
method panics with a generic message when the variable is of None
variant
println!("Value of variable a => {}", b.unwrap());
unwrap_or method
unwrap_or
method returns value of variable OR specified value
println!("Value of variable a => {}", a.unwrap_or(0));
unwrap_or_default method
unwrap_or_default
method returns value of variable OR default value of underlying type
println!("Value of variable a => {}", a.unwrap_or_default());
unwrap_or_else method
unwrap_or_else
method returns value of variable OR returns the value of the function argument
println!("Value of variable a => {}", a.unwrap_or_else(|| 10));
Comparing Option Variables
It is possible to compare 2 option variables in Rust
if a > b {
println!("Variable value a is greater than value of variable b");
} else {
println!("Variable value a is less than value of variable b");
}
Iterating over Option
An Option
can be iterated over. It is possible to call FromIterator
trait's method on an Option. In case if an Option
array contains None
, the resulted operation would be None
as well.
In this below example, we're creating an Option array having mixed of Some
and None
variants
let o_arr = [Some(10), Some(20), None, Some(30)];
Collecting elements from an Option array
We'll apply FromIterator
trait's into_iter
method and call collect
method on it. This will result in None
variant
let result_1: Option<Vec<i32>> = o_arr.into_iter().collect();
println!("Collect the elements => {result_1:?}");
Filter Option array and collect elements
We'll apply FromIterator
trait's filter
method and call collect
method on it. This time, the result will be Some<Vec<i32>>
let result_2: Option<Vec<i32>> = o_arr.into_iter().filter(|x| x.is_some()).collect();
println!("Filter & collect the elements => {result_2:?}");
Sum method on an Option array
We'll apply FromIterator
trait's sum
method and as it is having None
variant, the result will be of None
variant
let result_3: Option<i32> = o_arr.into_iter().sum();
println!("Sum of all elements without filter => {result_3:?}");
Product method on an Option array
We'll apply FromIterator
trait's product
method and as it is having None
variant, the result will be of None
variant
let result_4: Option<i32> = o_arr.into_iter().product();
println!("Product of all elements without filter => {result_4:?}");
Filter & Sum method on an Option array
Filter the option array and then call FromIterator
trait's sum
method. The result will be of Some<i32>
variant
let result_3: Option<i32> = o_arr.into_iter().filter(|x| x.is_some()).sum();
println!("Sum of all elements after filter => {result_3:?}");
Filter & Product method on an Option array
Filter the option array and then call FromIterator
trait's product
method. The result will be of Some<i32>
variant
let result_4: Option<i32> = o_arr.into_iter().filter(|x| x.is_some()).product();
println!("Product of all elements after filter => {result_4:?}");
I hope this blog post gives you a brief overview about Options.
All the code examples can be found in this link.
Please feel free to share your feedback.
Happy reading!!!
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