Type inference in Rust - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is type inference in Rust?

Type inference is Rust's ability to automatically figure out the type of a variable based on the value assigned to it, so you don't always have to write the type explicitly.

beginner

How does Rust infer the type of <code>let x = 5;</code>?

Rust sees the value 5 is an integer, so it infers that x is of type i32 by default.

intermediate

Can Rust infer types for function return values without explicit annotations?

Yes, Rust can infer the return type if it can figure it out from the function body, but sometimes you need to specify it for clarity or when inference is not possible.

intermediate

What happens if Rust cannot infer a variable's type?

Rust will give a compile-time error asking you to specify the type explicitly because it needs to know the exact type to ensure safety.

beginner

Example: What type does Rust infer for <code>let name = "Alice";</code>?

Rust infers the type as &str, which is a string slice pointing to a string literal.

What type does Rust infer for let num = 10; if no type is specified?

A String

B f64

C i32

D bool

Rust defaults integer literals to type i32 unless specified otherwise.

If Rust cannot infer a variable's type, what will happen?

A It will throw a compile-time error.

B It will guess the type randomly.

C It will assign the type as 'any'.

D It will run the program anyway.

Rust requires explicit types if it cannot infer them and will not compile without them.

Which of these can Rust infer the type for automatically?

A Function return type when it is clear.

B Type of a variable declared but never assigned.

C Type of a variable assigned from user input without parsing.

D Type of a variable assigned from a function with multiple return types.

Rust can infer return types when the function body clearly shows the type.

What type does Rust infer for let flag = true;?

A i32

B bool

C String

D char

The value true is a boolean, so Rust infers the type bool.

Why is type inference helpful in Rust?

A It removes the need for types completely.

B It slows down the compiler.

C It allows variables to change type at runtime.

D It makes code shorter and easier to read.

Type inference reduces the need to write types explicitly, making code cleaner and easier to write.

Explain what type inference is in Rust and give an example.

Think about how Rust figures out variable types without you writing them.

Describe a situation where Rust cannot infer a type and what you should do.

When Rust is unsure, it asks you to help by writing the type.