Variable shadowing in Rust - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is variable shadowing in Rust?

Variable shadowing in Rust means declaring a new variable with the same name as a previous variable. The new variable temporarily hides the old one within its scope.

intermediate

How does shadowing differ from mutability in Rust?

Shadowing lets you reuse a variable name by creating a new variable, even if the original was immutable. Mutability changes the value of the same variable without creating a new one.

intermediate

What happens if you shadow a variable with a different type?

Rust allows shadowing with a different type. The new variable can have a different type than the original, enabling transformations like converting a string to a number.

beginner

Consider this Rust code:<br><pre>let x = 5;<br>let x = x + 1;<br>let x = x * 2;<br>println!("{}", x);</pre><br>What is the output?

The output is 12.<br>Explanation:<br>- First x is 5.<br>- Then shadowed x is 6 (5 + 1).<br>- Then shadowed x is 12 (6 * 2).<br>- Finally, 12 is printed.

beginner

Why is variable shadowing useful in Rust?

Shadowing helps keep code clean by reusing variable names for updated values without needing new names. It also allows changing types safely and avoids mutability when not needed.

What does variable shadowing allow you to do in Rust?

A Declare a new variable with the same name as an existing one

B Change the value of a mutable variable

C Delete a variable from memory

D Create a global variable

Variable shadowing lets you declare a new variable with the same name, hiding the old one temporarily.

Can you shadow a variable with a different type in Rust?

A Only if the variable is mutable

B Yes, Rust allows changing the type when shadowing

C No, the type must stay the same

D Only inside functions

Rust permits shadowing with a different type, enabling type transformations.

What will this Rust code print?<br>

let a = 3;<br>let a = a * 4;<br>println!("{}", a);

A 3

B 7

C 12

D Error

The variable a is shadowed and updated to 12 (3 * 4), which is printed.

Which of these is NOT true about shadowing in Rust?

A Shadowing hides the previous variable temporarily

B Shadowing can change the variable's type

C Shadowing creates a new variable

D Shadowing requires the variable to be mutable

Shadowing does NOT require mutability; it works even with immutable variables.

Why might you prefer shadowing over mutability?

A To keep variables immutable and avoid bugs

B To make variables global

C To delete variables

D To speed up the program

Shadowing lets you update values while keeping variables immutable, which can reduce bugs.

Explain variable shadowing in Rust and give a simple example.

Think about declaring the same variable name twice.

Describe the benefits of using variable shadowing instead of mutability in Rust.

Why might you want to avoid mutable variables?