Lifetimes in structs in Rust - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a lifetime in Rust?

A lifetime in Rust is a way to tell the compiler how long a reference should be valid. It helps prevent dangling references and ensures memory safety.

beginner

Why do structs sometimes need lifetime annotations?

Structs need lifetime annotations when they hold references. This tells Rust how long those references are valid, so the compiler can check safety.

beginner

How do you declare a struct with a lifetime parameter?

You add a lifetime parameter with an apostrophe before the lifetime name, like struct MyStruct<'a> { field: &'a str }. This means the field's reference lives at least as long as 'a.

intermediate

What happens if you omit lifetime annotations on references in structs?

Rust will give a compile error because it can't be sure how long the references live. You must specify lifetimes to avoid dangling references.

intermediate

Explain the difference between &'a T and T in a struct field.

&'a T is a reference with a lifetime 'a, meaning it borrows data that lives at least as long as 'a. T owns the data directly, so no lifetime is needed.

Why do you add a lifetime parameter to a struct in Rust?

A To allow the struct to own data

B To make the struct mutable

C To specify how long references inside the struct are valid

D To enable multithreading

Lifetime parameters tell Rust how long references inside the struct must be valid to ensure safety.

What does the syntax &'a str mean in a struct field?

A A reference to a string slice valid for lifetime 'a

B An owned string with lifetime 'a

C A mutable string reference

D A static string

It means a reference to a string slice that lives at least as long as the lifetime 'a.

What error occurs if you forget to add lifetime annotations to references in structs?

A Compile error about missing lifetime specifier

B Runtime error

C Warning only, code compiles

D No error, Rust infers lifetimes automatically

Rust requires explicit lifetime annotations on references in structs to ensure safety.

Which of these is a correct way to declare a struct with a lifetime?

A struct Example { field: &i32 }

B struct Example<'a> { field: &'a i32 }

C struct Example<'a> { field: i32 }

D struct Example { field: &'a i32 }

You must declare the lifetime parameter 'a on the struct and use it on the reference.

What does the lifetime parameter 'a guarantee?

A The reference is mutable

B The reference is static

C The data is owned by the struct

D The reference lives at least as long as 'a

The lifetime 'a means the reference must be valid for at least the lifetime 'a.

Explain why lifetime annotations are necessary in structs that hold references.

Think about how Rust ensures memory safety with references inside structs.

Describe how to declare a struct with a lifetime parameter and a reference field.

Focus on the syntax for lifetime parameters and reference fields.