Variable lifetime basics in Rust - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a variable lifetime in Rust?

A variable lifetime is the period during which a variable is valid and can be used in the program. It starts when the variable is created and ends when it goes out of scope.

beginner

Why does Rust use lifetimes?

Rust uses lifetimes to ensure references are always valid and to prevent bugs like dangling pointers by checking how long references live at compile time.

beginner

What happens if a reference outlives the data it points to?

Rust will give a compile-time error because the reference would be invalid, preventing unsafe memory access.

intermediate

How do you specify a lifetime in a function signature?

You use an apostrophe followed by a name, like &'a, to tell Rust that the reference has a certain lifetime named 'a.

beginner

What is the scope of a variable in Rust?

The scope is the part of the code where the variable is accessible. When the scope ends, the variable is dropped and its lifetime ends.

What does a variable lifetime represent in Rust?

A The time a variable is valid and accessible

B The size of the variable in memory

C The number of times a variable is used

D The type of the variable

A variable lifetime is the period during which the variable is valid and can be accessed.

Why does Rust enforce lifetimes on references?

A To allow variables to change type

B To make the code run faster

C To prevent invalid references and memory bugs

D To increase the size of the program

Rust uses lifetimes to ensure references do not outlive the data they point to, preventing bugs.

What symbol is used to name a lifetime in Rust?

A #

B &

C $

D '

Lifetimes are named using an apostrophe, like 'a, in Rust.

What happens if a reference's lifetime is longer than the data it points to?

A Rust allows it without warnings

B Rust gives a compile-time error

C The program crashes at runtime

D The reference is automatically copied

Rust prevents this by giving a compile-time error to avoid invalid memory access.

When does a variable's lifetime end in Rust?

A When the variable goes out of scope

B When the variable is reassigned

C When the program finishes

D When the variable is printed

A variable's lifetime ends when it goes out of scope, meaning it is no longer accessible.

Explain what a variable lifetime is and why it matters in Rust.

Think about how long a variable can be used safely.

Describe how Rust uses lifetimes to prevent bugs with references.

Focus on how Rust checks references before running the program.