Generic enums in Rust - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a generic enum in Rust?

A generic enum in Rust is an enum that can hold different types specified by a generic parameter. It allows the enum to be flexible and work with various data types.

beginner

How do you define a generic enum with one type parameter in Rust?

You add a type parameter inside angle brackets after the enum name, like <T>. For example: <br>

enum Option<T> {
    Some(T),
    None,
}

intermediate

Why use generic enums instead of fixed-type enums?

Generic enums let you write one enum that works with many types, reducing code duplication and increasing flexibility. For example, Option<T> can hold any type T, not just one fixed type.

intermediate

Can generic enums have multiple type parameters? Give an example.

Yes, generic enums can have multiple type parameters. Example:<br>

enum Result {
    Ok(T),
    Err(E),
}

This enum can hold a success value of type T or an error value of type E.

beginner

How do you create an instance of a generic enum with a specific type?

You specify the type when you use the enum. For example:<br><pre>let x: Option<i32> = Option::Some(5);</pre> Here, Option is used with i32 as the type parameter.

What does the <T> mean in enum Option<T>?

A It declares a generic type parameter T for the enum.

B It is a syntax error in Rust.

C It means the enum only works with type T fixed as integer.

D It is a lifetime parameter.

The declares a generic type parameter, allowing the enum to hold any type specified when used.

Which of these is a valid generic enum definition?

A enum Result { Ok<T>, Err<E> }

B enum Result<T, E> { Ok(T), Err(E) }

C enum Result<T> { Ok, Err }

D enum Result<T, E> { Ok, Err }

Option B correctly defines a generic enum with two type parameters and variants holding those types.

How do you create an Option holding a string "hello"?

A Option::Some("hello")

B Option::Some(hello)

C Option::None("hello")

D Option::Some<String>

Option::Some("hello") creates an Option holding a string slice. The type is inferred or can be specified explicitly.

What is the benefit of using generic enums?

A They restrict enums to only one data type.

B They make enums slower.

C They allow enums to work with multiple data types without rewriting code.

D They are only used for error handling.

Generic enums increase flexibility by allowing the same enum to hold different types.

Can you use a generic enum without specifying the type parameter?

A Only if the enum has no variants.

B Yes, Rust assumes a default type.

C Yes, generic enums do not require type parameters.

D No, you must specify or let Rust infer the type.

You must specify the type parameter or let Rust infer it from context.

Explain what a generic enum is and why it is useful in Rust.

Think about how enums can hold different types using generics.

Write a simple generic enum with two variants and explain how to create an instance of it.

Use something like Result<T, E> or Option<T>.