Collection mutability tied to let/var in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What happens when you declare a collection with let in Swift?

Declaring a collection with let makes it immutable. You cannot add, remove, or change elements after initialization.

beginner

How does declaring a collection with var affect its mutability?

Declaring a collection with var makes it mutable. You can add, remove, or modify elements freely.

intermediate

Can you modify the elements of a collection declared with let if the elements themselves are reference types?

Yes, if the elements are reference types (like classes), you can modify their internal properties even if the collection is declared with let. But you cannot change the collection structure itself.

beginner

Why does Swift tie collection mutability to let and var?

Swift uses let and var to clearly express intent. let means the collection won't change, helping prevent bugs. var allows changes when needed.

beginner

What error occurs if you try to modify a let-declared collection?

You get a compile-time error saying you cannot use mutating methods on an immutable value.

What does declaring an array with let in Swift mean?

A The array can be changed anytime

B The array elements can be changed but not the array size

C The array is deleted automatically

D The array cannot be changed after creation

Declaring with let makes the array immutable, so you cannot add, remove, or change elements.

If you declare a dictionary with var, what can you do?

A Only read elements

B Only remove elements

C Add, remove, or modify elements

D Only add elements

Using var allows full mutability of the collection.

Can you modify the properties of class instances inside a let-declared array?

A Yes, properties of class instances can be changed

B No, nothing can be changed

C Only if the array is declared with <code>var</code>

D Only if the class is a struct

The collection is immutable, but the reference type elements can have their properties changed.

What keyword in Swift declares a mutable collection?

A let

B var

C const

D mutable

var declares a mutable collection.

What kind of error do you get if you try to append to a let-declared array?

A Compile-time error

B Runtime error

C No error

D Logical error

Swift prevents this at compile time to avoid mutating an immutable collection.

Explain how let and var affect collection mutability in Swift.

Think about whether you can change the collection after creating it.

Describe what happens when you try to modify a let-declared collection and why Swift enforces this.

Consider Swift's goal to avoid bugs by enforcing immutability.