Is operator for type checking in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the is operator do in Swift?

The is operator checks if an instance is of a certain type or inherits from that type. It returns true if the instance matches the type, otherwise false.

beginner

How do you use the is operator in an if statement?

You write: if object is SomeType { /* code */ }. This runs the code inside the block only if object is of type SomeType or a subclass.

intermediate

Can the is operator check for protocol conformance?

Yes! The <code>is</code> operator can check if an instance conforms to a protocol, not just class or struct types.

intermediate

What is the difference between is and as? in Swift?

is checks if an instance is of a type and returns a Boolean. as? tries to cast the instance to that type and returns an optional value.

beginner

Example: What does this code print?<br><pre>let value: Any = 5<br>if value is Int { print("It's an Int") }</pre>

It prints: It's an Int because the value 5 is an integer and the is operator confirms that.

What does the is operator return when used in Swift?

A The memory address of the instance

B The instance cast to the specified type

C The size of the instance in bytes

D A Boolean indicating if the instance matches the type

The is operator returns true or false depending on whether the instance is of the specified type.

Which of these can the is operator check for?

A Protocol conformance

B Class type only

C Variable value

D Function return type

The is operator can check if an instance conforms to a protocol.

What will this code print?<br>

let text: Any = "Hello"<br>if text is String { print("It's a String") }

A Error

B Nothing

C It's a String

D It's an Int

The variable text holds a string, so text is String is true.

What is the result of value is Double if value is an Int?

A true

B false

C Runtime error

D Optional Double

An Int is not a Double, so the check returns false.

Which operator tries to convert an instance to a type and returns an optional?

A as?

B is

C ==

D !=

as? attempts to cast and returns an optional value.

Explain how the is operator works in Swift and give a simple example.

Think about how you check if something is a certain kind of thing in real life.

Describe the difference between is and as? operators in Swift.

One checks type, the other tries to change type.