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

Madhurig at 08:52, 29 August 2025

2025-08-29T08:52:23Z

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Nirmala Venkat: Created page with "{| border="1" |- || '''Visual Cue''' || '''Narration''' |- || '''Slide 1''' || Welcome to the Spoken Tutorial on
2025-08-22T13:04:48Z

Created page with "{| border="1" |- || '''Visual Cue''' || '''Narration''' |- || '''Slide 1''' || <span style="color:#000000;">Welcome to the Spoken Tutorial on </span><span style="color:#00000..."

New page
{| border="1"
|-
|| '''Visual Cue'''
|| '''Narration'''
|-

|| '''Slide 1'''
|| <span style="color:#000000;">Welcome to the Spoken Tutorial on </span><span style="color:#000000;">'''Pattern Matching '''</span><span style="color:#000000;">in </span><span style="color:#000000;">'''Rust.'''</span>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
|| <div style="color:#000000;">Slide 2:</div>

<div style="color:#000000;">Learning Objective</div>
|| In this tutorial, we will learn about
* <div style="color:#000000;margin-left:1.27cm;margin-right:0cm;">Pattern matching</div>

|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.171cm;padding-right:0.191cm;"
|| <div style="color:#000000;">Slide:</div>

<div style="color:#000000;">Code Files</div>
||
* <div style="color:#000000;margin-left:1.27cm;margin-right:0cm;">The following code file is required to practise this tutorial</div>
* <div style="color:#000000;margin-left:1.27cm;margin-right:0cm;">This file is provided in the code files link of this tutorial page</div>

|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
|| <div style="color:#000000;">'''Slide:'''</div>

<div style="color:#000000;">'''Pattern Matching syntax:'''</div>

<div style="color:#000000;">'''match VALUE {'''</div>

<div style="color:#000000;">'''PATTERN => EXPRESSION,'''</div>

<div style="color:#000000;">'''PATTERN => EXPRESSION,'''</div>

<div style="color:#000000;">'''PATTERN => EXPRESSION,'''</div>

<div style="color:#000000;">'''}'''</div>
|| This is the syntax for the pattern matching.
* <div style="margin-left:1.27cm;margin-right:0cm;">The '''match''' statement is a powerful control flow </div>
* <div style="margin-left:1.27cm;margin-right:0cm;">It allows you to compare a value against a series of patterns </div>
* <div style="margin-left:1.27cm;margin-right:0cm;">It executes the code based on which pattern matches.</div>
* <div style="margin-left:1.27cm;margin-right:0cm;">It is similar to the '''Switch''' statement in other languages.</div>

|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
| style="color:#000000;" | Open Visual code editor
|| <span style="color:#000000;">Let us open the </span><span style="color:#000000;">'''visual code editor'''</span><span style="color:#000000;"> and understand how pattern matching works.</span>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
| style="color:#000000;" | >cd Desktop/MyRustProject
|| <span style="color:#000000;">Go to our working directory </span><span style="color:#000000;">'''MyRustProject'''</span><span style="color:#000000;"> as explained earlier.</span>

<span style="color:#000000;">Type the command </span><span style="color:#000000;">'''cargo new </span><span style="color:#000000;">pattern'''</span>

<div style="color:#000000;">Open the created project.</div>

<span style="background-color:#ffffff;color:#000000;">In the </span><span style="background-color:#ffffff;color:#000000;">'''main.rs '''</span><span style="background-color:#ffffff;color:#000000;">file, replace the </span><span style="background-color:#ffffff;color:#000000;">'''code'''</span><span style="background-color:#ffffff;color:#000000;"> </span><span style="background-color:#ffffff;color:#000000;">as shown.</span>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
|| <div style="color:#252525;">fn main() {</div>

<div style="color:#252525;">let x = 3;</div>

<div style="color:#252525;">match x {</div>

<div style="color:#252525;">1 => println!("One!"),</div>

<div style="color:#252525;">2 => println!("Two!"),</div>

<div style="color:#252525;">3 => println!("Three!"),</div>

<div style="color:#252525;">_ => println!("Something else!"),</div>

<div style="color:#252525;">}</div>

<div style="color:#252525;">}</div>
|| <span style="color:#252525;">The </span><span style="color:#111111;">'''match'''</span><span style="color:#252525;"> </span><span style="color:#252525;">statement is used to compare </span><span style="color:#111111;">'''x</span><span style="color:#252525;"> '''</span><span style="color:#252525;">against different patterns i.e </span><span style="color:#111111;">(1</span><span style="color:#111111;"> or </span><span style="color:#111111;">2</span><span style="color:#111111;"> or </span><span style="color:#111111;">3).</span>

<span style="color:#252525;">'''underscore'''</span><span style="color:#252525;"> </span><span style="color:#252525;">'''pattern '''</span><span style="color:#252525;">is a </span><span style="color:#252525;">'''catch-all pattern.'''</span>
<span style="color:#252525;">It</span><span style="color:#252525;"> matches any other value not explicitly covered by previous patterns. </span>

<span style="color:#111111;">In this case, it will print "Something else!",</span><span style="color:#111111;"> </span><span style="color:#111111;">if x</span><span style="color:#111111;"> </span><span style="color:#111111;">is not 1, 2, or 3. </span>

<div style="color:#111111;">Save the code. Let us execute and see the result.</div>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
| style="color:#000000;" |
|| <span style="color:#000000;">In the menu bar, click on terminal and select </span><span style="color:#000000;">'''New Terminal.'''</span>

|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
|| <span style="color:#000000;">Type</span><span style="color:#000000;"> </span><span style="color:#000000;">Cargo build</span>
|| <span style="color:#000000;">In the terminal, type </span><span style="color:#000000;">'''cargo run.'''</span>

We can see the output as ‘'''Three'''’ which matches the pattern as per the x value.

<div style="color:#000000;">Let us change the value of x to 10 in the code.</div>

<div style="color:#000000;"></div>
|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" |
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" | <div style="color:#000000;">Save the code and run the program.</div>

<div style="color:#000000;">We can see the output as '''“something else'''” as expected.</div>

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" |
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" | The most common case for pattern matching is with '''Option''' and '''Result''' enum types.
|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" | <div style="color:#000000;">'''Slide:'''</div>

<div style="color:#000000;">'''Matching Option and Result type'''</div>
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" |

<span style="color:#000000;">'''Option'''</span><span style="color:#000000;"> and </span><span style="color:#000000;">'''Result'''</span><span style="color:#000000;"> type have two variants.</span>

<div style="color:#000000;">'''Option''' type has:</div>

<div style="color:#000000;">None →It is used to indicate failure with no value</div>

<div style="color:#000000;">Some(T) → It returns a value with type T</div>

<div style="color:#000000;">'''Result''' type has:</div>

<div style="color:#000000;">Ok(T) → It indicates operation succeeded with value T</div>

<div style="color:#000000;">Err(E) → It indicates operation failed with an error E</div>

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;color:#000000;" |
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" | <span style="color:#000000;">Let us see an example </span>for<span style="color:#000000;"> </span><span style="color:#000000;">'''Matching Option Type '''</span><span style="color:#000000;">in Rust.</span>

<span style="color:#000000;">Switch back to the </span><span style="color:#000000;">V</span><span style="color:#000000;">isual </span><span style="color:#000000;">Co</span><span style="color:#000000;">de editor.</span>
|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" | <div style="color:#000000;">'''fn main() {'''</div>

<div style="color:#000000;">'''fn first_element(array: &[i32]) -> Option<i32> {'''</div>

<div style="color:#000000;">'''if array.len() > 0 {'''</div>

<div style="color:#000000;">'''Some(array[0])'''</div>

<div style="color:#000000;">'''} else {'''</div>

<div style="color:#000000;">'''None'''</div>

<div style="color:#000000;">'''}'''</div>

<div style="color:#000000;">'''}'''</div>

<div style="color:#000000;">'''let array = [];'''</div>

<div style="color:#000000;">'''println!("{:?}", first_element(&array));'''</div>

<div style="color:#000000;">'''}'''</div>
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" | <div style="color:#000000;">Copy and paste the code from the codefile.</div>

<span style="color:#252525;">Here the </span><span style="color:#252525;">function </span><span style="color:#188038;">first_element</span><span style="color:#252525;">, returns the first element of an integer array if it exists. </span>

It takes a reference to an array of integers <span style="color:#c9211e;">(&[i32])</span> as its parameter and returns an <span style="color:#6aa84f;">Option<</span><span style="color:#c9211e;">i32</span><span style="color:#6aa84f;">>.</span>

<span style="color:#252525;">The function checks the length of the array using </span><span style="color:#188038;">array.len()</span><span style="color:#252525;">. </span>

<span style="color:#252525;">If the array has one or more elements, it returns</span><span style="color:#252525;"> </span><span style="color:#188038;">S</span><span style="color:#188038;">ome(array[0])</span><span style="color:#252525;">, i.e </span><span style="color:#252525;">the first element of the array. </span>

<span style="color:#252525;">If the array is empty, it returns </span><span style="color:#188038;">None</span><span style="color:#252525;">, indicating that there is no first element to return.</span>

<div style="color:#000000;">Save the file.</div>
|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;color:#000000;" |
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" | <div style="color:#000000;">In the terminal, type '''cargo run '''and see the output.</div>

<span style="background-color:transparent;color:#000000;">'''None'''</span><span style="background-color:transparent;color:#000000;"> </span><span style="background-color:transparent;color:#000000;">is displayed as output as the array is empty in the program.</span>
|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;color:#000000;" |
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" | <span style="background-color:transparent;color:#000000;">Let us add 10,20,30 as array elements in the code.</span>

<span style="background-color:transparent;color:#000000;">Save the program and run it again.</span>

<span style="background-color:transparent;color:#000000;">Now it displays the first element of the array as 10.</span>
|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;color:#000000;" |
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" | <span style="color:#000000;">Next we will see </span>about the '''Result<span style="color:#000000;"> enum '''</span><span style="color:#000000;">type.</span>
|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" | <div style="color:#252525;">fn main() {</div>

<div style="color:#252525;">fn divide(dividend: i32, divisor: i32) -> Result<i32, String> {</div>

<div style="color:#252525;">if divisor == 0 {</div>

<div style="color:#252525;">Err(String::from("Cannot divide by zero"))</div>

<div style="color:#252525;">} else {</div>

<div style="color:#252525;">Ok(dividend / divisor)</div>

<div style="color:#252525;">}</div>

<div style="color:#252525;">}</div>

<div style="color:#252525;">let result = divide(10, 2);</div>

<div style="color:#252525;">match result {</div>

<div style="color:#252525;">Ok(value) => println!("Result: {}", value),</div>

<div style="color:#252525;">Err(error) => println!("Error: {}", error),}</div>

| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" | <div style="color:#000000;">Copy and paste the code from the codefile.</div>

<div style="color:#252525;">The result enum has two variants representing a correct value and an Error.</div>

<span style="color:#252525;">Here, we define a function </span><span style="color:#188038;">divide</span><span style="color:#252525;"> that performs division.</span>

<span style="color:#252525;">It returns a </span><span style="color:#188038;">Result</span><span style="color:#252525;"> enum to indicate success or failure.</span>

<span style="color:#252525;">The </span><span style="color:#188038;">divide</span><span style="color:#252525;"> function takes two parameters: </span><span style="color:#188038;">dividend</span><span style="color:#252525;"> and </span><span style="color:#188038;">divisor</span><span style="color:#252525;">, both of type </span><span style="color:#188038;">i32</span><span style="color:#252525;">. </span>

<span style="color:#252525;">It returns a </span><span style="color:#188038;">Result<i32, String>. </span>

<span style="color:#000000;">It</span><span style="color:#188038;"> </span><span style="color:#000000;">can</span><span style="color:#188038;"> </span><span style="color:#000000;">be</span><span style="color:#252525;"> </span><span style="color:#188038;">Ok </span><span style="color:#252525;">on success i.e (the result of the division).</span>

<span style="color:#252525;">Otherwise it returns</span><span style="color:#252525;"> </span><span style="color:#188038;">Err(String)</span><span style="color:#252525;"> if an error occurs i.e(like division by zero).</span>

<span style="color:#000000;">Save th</span>e file.
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
||
|| Run the code and see the output

<span style="background-color:transparent;color:#000000;">It displays 5 as the result of the division.</span>
|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" |
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;" | <span style="background-color:transparent;color:#000000;">Change the parameters in the divide function as (10,0).</span>

<span style="background-color:transparent;color:#000000;">Save the program and run it again.</span>

<div style="color:#000000;">It displays the error message.</div>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
| style="color:#000000;" |
|| <div style="color:#000000;">This brings us to the end of this tutorial.</div>

<div style="color:#000000;">Let us summarize. </div>
|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
| style="color:#000000;" |
|| In this tutorial, we learn about
* <div style="margin-left:1.27cm;margin-right:0cm;">Pattern matching</div>

|- style="border:1pt solid #000000;padding-top:0cm;padding-bottom:0cm;padding-left:0.206cm;padding-right:0.191cm;"
| style="color:#000000;" | Thank You
| style="color:#000000;" | Thanks for joining.
|-
|}
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