Basic match usage in Rust - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the match statement in Rust?

The match statement lets you compare a value against many patterns and execute code based on which pattern matches. It's like a more powerful switch in other languages.

beginner

How do you write a simple match expression to check if a number is 1, 2, or something else?

Example:<br>

match number {
    1 => println!("One"),
    2 => println!("Two"),
    _ => println!("Other"),
}

<br>The underscore _ means "anything else".

beginner

What does the underscore _ pattern mean in a match?

It means "match anything else". It's a catch-all pattern used when you don't want to specify all possible cases.

intermediate

Can match return a value in Rust? How?

Yes! <code>match</code> is an expression, so it returns the value of the matched arm. For example:<br><pre>let result = match x {
    1 => "one",
    _ => "other",
};</pre>

beginner

What happens if you don't cover all possible cases in a match?

Rust will give a compile error because match must be exhaustive. You must cover all cases or use _ to catch the rest.

What does the _ pattern do in a Rust match?

A Causes a compile error

B Matches only zero

C Matches any value not matched before

D Matches only negative numbers

The underscore _ is a catch-all pattern that matches any value not matched by previous arms.

Which of these is a valid match arm syntax?

A if 1 { println!("One") }

B case 1: println!("One")

C when 1 => println!("One")

D 1 => println!("One")

Rust uses the syntax pattern => expression in match arms.

What will this code print?<br>

let x = 3;
match x {
  1 => println!("One"),
  2 => println!("Two"),
  _ => println!("Other"),
}

A Other

B One

C Two

D Compile error

Since 3 matches no specific arm, the _ arm runs, printing "Other".

Can match be used to assign a value to a variable?

A Yes, because <code>match</code> is an expression

B No, <code>match</code> only controls flow

C Only if you use <code>if</code> inside <code>match</code>

D Only with <code>return</code>

match returns the value of the matched arm, so you can assign it to variables.

What happens if you forget to cover all cases in a match?

A Rust compiles silently

B Rust gives a compile error

C Rust compiles but warns

D Rust runs but panics at runtime

Rust requires match to be exhaustive and will not compile if some cases are missing.

Explain how the match statement works in Rust and why it is useful.

Think about how <code>match</code> compares values and handles all possibilities.

Write a simple Rust match expression that prints "small" for 1 or 2, "medium" for 3 or 4, and "large" for anything else.

Use | to combine patterns for the same arm.