Matching multiple patterns in Rust - Step-by-Step Execution

Concept Flow - Matching multiple patterns

Start match expression

↓

Check first pattern

Yes↓

Execute first arm

↓

End

↓

Check second pattern

Yes↓

Execute second arm

↓

End

↓

Check next patterns...

↓

Default arm or error

The program checks each pattern in order. If the value matches any pattern in an arm, it runs that arm and stops matching.

Execution Sample

Rust

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

This code matches x against multiple patterns in one arm using | to combine them.

Execution Table

Step	Value of x	Pattern Checked	Match Result	Action Taken	Output
1	2	1 | 2	Match	Execute arm	One or Two
2	2	3	Not checked	No action
3	2	_	Not checked	No action

💡 Match found at first pattern (1 | 2), so matching stops.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
x	2	2	2	2

Key Moments - 2 Insights

Why does the program not check the second pattern when the first matches?

Because Rust stops matching once it finds a matching pattern, as shown in execution_table step 1 where the first pattern matches and later patterns are not checked.

How do we match multiple values in one arm?

By using the | symbol between patterns, like 1 | 2, which means match if value is 1 or 2, as seen in execution_table step 1.

Visual Quiz - 3 Questions

Look at the execution table, what is the output at step 1?

A "One or Two"

B "Three"

C "Other"

D No output

💡 Hint

Check the 'Output' column in execution_table row 1.

At which step does the program stop checking patterns?

A Step 3

B Step 2

C Step 1

D It checks all steps

💡 Hint

See 'Match Result' and 'Action Taken' in execution_table; matching stops at first match.

If x was 3, which pattern would match according to the table?

A 1 | 2

B 3

C _

D No pattern matches

💡 Hint

Look at the patterns and think which matches value 3.

Concept Snapshot

match value {
  pattern1 | pattern2 => action,
  pattern3 => action,
  _ => default_action,
}
- Use | to match multiple patterns in one arm.
- Matching stops at first successful pattern.
- _ matches anything else.

Full Transcript

This example shows how Rust matches a value against multiple patterns using the | symbol. The program checks each pattern in order. If the value matches any pattern in an arm, it runs that arm and stops matching further. For example, when x is 2, it matches the first arm with patterns 1 or 2, prints "One or Two", and stops. This prevents checking other patterns unnecessarily. Using | lets you combine multiple values in one match arm for cleaner code.