Destructuring patterns in Rust - Step-by-Step Execution

Concept Flow - Destructuring patterns

Start with a value

↓

Apply destructuring pattern

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Extract parts into variables

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Use extracted variables

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End

Destructuring patterns break a value into parts and assign them to variables step-by-step.

Execution Sample

Rust

let (x, y) = (10, 20);
println!("x = {}, y = {}", x, y);

This code splits a tuple into two variables x and y, then prints them.

Execution Table

Step	Action	Pattern	Value	Variables Assigned
1	Start with tuple value	(x, y)	(10, 20)	none
2	Match pattern to value	(x, y)	(10, 20)	x = 10, y = unassigned
3	Assign y from tuple	(x, y)	(10, 20)	x = 10, y = 20
4	Use variables	N/A	N/A	Print x=10, y=20
5	End	N/A	N/A	Variables x=10, y=20 in scope

💡 All parts of the tuple matched and assigned, execution ends.

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
x	unassigned	10	10	10
y	unassigned	unassigned	20	20

Key Moments - 2 Insights

Why is y unassigned after step 2 but assigned after step 3?

Step 2 starts matching the pattern but only assigns x first; y is assigned in step 3 as the pattern matches the second tuple element (see execution_table rows 2 and 3).

What happens if the pattern and value lengths don't match?

Rust will give a compile-time error because the destructuring pattern must match the value structure exactly (not shown here but important to know).

Visual Quiz - 3 Questions

Look at the execution table, what is the value of x after step 3?

A 10

B 20

C unassigned

D None

💡 Hint

Check the 'Variables Assigned' column in row 3 of the execution_table.

At which step are both x and y assigned values?

A Step 2

B Step 3

C Step 4

D Step 1

💡 Hint

Look at the 'Variables Assigned' column to see when both variables have values.

If the tuple was (10, 20, 30), what would happen to the destructuring pattern (x, y)?

A x=10, y=20, 30 ignored

B x=10, y=30

C Compile-time error due to mismatch

D x=20, y=30

💡 Hint

Rust requires pattern and value to match exactly; extra elements cause errors.

Concept Snapshot

Destructuring patterns let you split complex values into parts.
Syntax: let (a, b) = (1, 2);
Each pattern part matches a value part.
All parts must match exactly.
Variables get assigned in order.
Use destructuring to simplify code.

Full Transcript

This visual trace shows how destructuring patterns work in Rust. We start with a tuple (10, 20). The pattern (x, y) matches this tuple. Step 2 assigns x to 10, step 3 assigns y to 20. After both assignments, we can use x and y as separate variables. If the pattern and value don't match in size, Rust will give an error. This helps break down values simply and safely.