Match overview in Rust - Step-by-Step Execution

Concept Flow - Match overview

Start: Have a value

↓

Match value against patterns

↓

Check pattern 1

No→Check pattern 2

↓

Execute code block

↓

End

The match expression checks a value against multiple patterns one by one and runs the code for the first matching pattern.

Execution Sample

Rust

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

This code matches the variable 'number' against patterns 1, 2, and a default, printing the matching case.

Execution Table

Step	Matched Value	Pattern Checked	Match Result	Action Taken	Output
1	2	1	No	Check next pattern
2	2	2	Yes	Execute println!("Two")	Two
3	2	_ (default)	Skipped	No action
4	2	End	Match found, exit	Stop matching

💡 Match found at pattern 2, so matching stops.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
number	2	2	2	2

Key Moments - 2 Insights

Why does the match stop checking after finding the first match?

Because Rust's match expression runs only the first matching pattern's code and then exits, as shown in execution_table step 4.

What does the underscore (_) pattern mean in a match?

It means 'any other value' and acts as a default case if no previous patterns match, as seen in execution_table step 3.

Visual Quiz - 3 Questions

Look at the execution table, what pattern matches the value 2?

A Pattern 1

B Default (_) pattern

C Pattern 2

D No pattern matches

💡 Hint

Check the 'Match Result' column in execution_table row 2.

At which step does the match expression stop checking patterns?

A Step 4

B Step 2

C Step 1

D Step 3

💡 Hint

Look at the 'Action Taken' and 'Match Result' columns in execution_table step 4.

If number was 5, which pattern would match?

A Pattern 2

B Default (_) pattern

C Pattern 1

D No pattern matches

💡 Hint

The default pattern matches any value not matched before, as explained in key_moments.

Concept Snapshot

match value {
    pattern1 => action1,
    pattern2 => action2,
    _ => default_action,
}

- Checks patterns top to bottom
- Runs first matching action
- '_' is default catch-all
- Stops after first match

Full Transcript

The Rust match expression compares a value against multiple patterns in order. It starts with the first pattern and checks if the value fits. If it does, it runs the code for that pattern and stops checking further. If not, it moves to the next pattern. The underscore (_) pattern is a default that matches anything not matched before. This way, match expressions let you run different code depending on the value, similar to a switch-case but more powerful and safe.