Basic match usage in Rust - Step-by-Step Execution

Concept Flow - Basic match usage

Start with a value

↓

match value with patterns

↓

Pattern 1?

Yes→Execute code 1

↓

Pattern 2?

Yes→Execute code 2

↓

Pattern 3?

Yes→Execute code 3

↓

Default pattern

→Execute default code

↓

End match

The match expression compares a value against 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 checks the value of 'number' and prints a message depending on which pattern matches.

Execution Table

Step	Value matched	Pattern checked	Match?	Action executed	Output
1	2	1	No	None
2	2	2	Yes	println!("Two")	Two
3	-	Default (_)	Skipped	None

💡 Match stops after the first successful pattern match (pattern 2).

Variable Tracker

Variable	Start	After match
number	2	2

Key Moments - 2 Insights

Why does the match stop after checking pattern 2 and not continue to the default?

Because match stops at the first pattern that matches the value, as shown in execution_table row 2 where pattern 2 matches and the default is skipped.

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

The underscore is a catch-all pattern that matches any value not matched by previous patterns, as seen in execution_table row 3.

Visual Quiz - 3 Questions

Look at the execution table, what pattern is checked first?

A Pattern 1

B Pattern 2

C Default (_)

D Pattern 3

💡 Hint

Check the 'Pattern checked' column in the first row of the execution_table.

At which step does the match find a successful pattern?

A Step 1

B Step 3

C Step 2

D No successful match

💡 Hint

Look at the 'Match?' column to find where it says 'Yes'.

If 'number' was 5, which pattern would match?

A Pattern 1

B Default (_)

C Pattern 2

D No pattern matches

💡 Hint

Refer to variable_tracker and the meaning of the underscore pattern in key_moments.

Concept Snapshot

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

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

Full Transcript

This example shows how Rust's match expression works. We start with a value 'number' set to 2. The match checks each pattern in order: first 1, then 2, then the default underscore. It finds that 2 matches pattern 2, so it runs the code to print "Two" and stops checking further patterns. The underscore pattern is a catch-all for any value not matched earlier. Variables keep their values unchanged during matching. This step-by-step trace helps understand how match chooses which code to run.