Rust-Programming-Language/C2/Pattern-Matching/English

Visual Cue	Narration
Slide 1	Welcome to the Spoken Tutorial on Pattern Matching in Rust.
Slide 2: Learning Objective	In this tutorial, we will learn about Pattern matching
Slide: Code Files	The following code file is required to practise this tutorial This file is provided in the code files link of this tutorial page
Slide: Pattern Matching syntax: match VALUE { PATTERN => EXPRESSION, PATTERN => EXPRESSION, PATTERN => EXPRESSION, }	This is the syntax for the pattern matching. The match statement is a powerful control flow It allows you to compare a value against a series of patterns It executes the code based on which pattern matches. It is similar to the Switch statement in other languages.
Open Visual code editor	Let us open the visual code editor and understand how pattern matching works.
>cd Desktop/MyRustProject	Go to our working directory MyRustProject as explained earlier. Type the command cargo new pattern Open the created project. In the main.rs file, replace the code as shown.
fn main() { let x = 3; match x { 1 => println!("One!"), 2 => println!("Two!"), 3 => println!("Three!"), _ => println!("Something else!"), } }	Thematch statement is used to comparex against different patterns that is 1 or 2 or 3. underscore pattern is a catch-all pattern. It matches any other value not explicitly covered by previous patterns. In this case, it will print "Something else!", if x is not 1, 2, or 3. Save the code. Let us execute and see the result.
Click on Terminal and select New Terminal.	In the menu bar, click on Terminal and select New Terminal.
Type Cargo build	In the terminal, type cargo run. We can see the output as ‘Three’ which matches the pattern as per the x value. Let us change the value of x to 10 in the code.
	Save the code and run the program. We can see the output as “something else” as expected.
	The most common case for pattern matching is with Option and Result enum types.
Slide: Matching Option and Result type	Option and Result type have two variants. Option type has: None → It is used to indicate failure with no value Some(T) → It returns a value with type T Result type has: Ok(T) → It indicates operation succeeded with value T Err(E) → It indicates operation failed with an error E
	Let us see an example for Matching Option Type in Rust. Switch back to the Visual Code editor.
fn main() { fn first_element(array: &[i32]) -> Option<i32> { if array.len() > 0 { Some(array[0]) } else { None } } let array = []; println!("{:?}", first_element(&array)); }	Clear the window and copy and paste the code from the code file. Here the function first_element, returns the first element of an integer array if it exists. It takes a reference to an array of integers (&[i32]) as its parameter and returns an Option <i32>. The function checks the length of the array using array.len(). If the array has one or more elements, it returns Some(array[0]), that is the first element of the array. If the array is empty, it returns None, indicating that there is no first element to return. Save the file.
Type cargo run and see the output.	In the terminal, type cargo run and see the output. None is displayed as output as the array is empty in the program.
Add 10,20,30 as array elements	Let us add 10,20,30 as array elements in the code. Save the program and run it again. Now it displays the first element of the array as 10.
	Next we will see about the Result enum type.
fn main() { fn divide(dividend: i32, divisor: i32) -> Result<i32, String> { if divisor == 0 { Err(String::from("Cannot divide by zero")) } else { Ok(dividend / divisor) } } let result = divide(10, 2); match result { Ok(value) => println!("Result: {}", value), Err(error) => println!("Error: {}", error),}	Clear the window and copy and paste the code from the code file. The result enum has two variants representing a correct value and an Error. Here, we define a function divide that performs division. It returns a Result enum to indicate success or failure. The divide function takes two parameters: dividend and divisor, both of type i32. It returns a Result of type <i32. It can be OK on success that is the result of the division. Otherwise it returns Err(String) if an error occurs, that is like division by zero. Save the file.
	Run the code and see the output It displays 5 as the result of the division.
	Change the parameters in the divide function as (10,0). Save the program and run it again. It displays the error message.
	This brings us to the end of this tutorial. Let us summarize.
	In this tutorial, we learn about Pattern matching
Thank You	Thanks for joining.

Contributors and Content Editors

Madhurig, Nirmala Venkat