In-out parameters for mutation in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an in-out parameter in Swift?

An in-out parameter allows a function to modify a variable passed to it, so the changes persist outside the function.

beginner

How do you declare an in-out parameter in a Swift function?

Use the inout keyword before the parameter type in the function definition.

beginner

How do you pass a variable as an in-out argument when calling a Swift function?

Use the ampersand & before the variable name to pass it as an in-out argument.

intermediate

Why can't you pass a constant or a literal as an in-out argument?

Because in-out parameters require the ability to modify the variable, constants and literals cannot be changed.

beginner

What happens if you forget to use & when passing an in-out argument?

The Swift compiler will give an error because it expects an explicit indication that the variable can be modified.

Which keyword is used to declare an in-out parameter in Swift?

A inout

B mutate

C var

D ref

The inout keyword marks a parameter that can be modified inside the function.

How do you pass a variable as an in-out argument when calling a function?

A With parentheses around the variable

B With an asterisk (*) before the variable

C Just the variable name

D With an ampersand (&) before the variable

You must use & before the variable name to indicate it can be modified.

Can you pass a constant as an in-out argument?

A Yes, always

B Only if the function returns a value

C No, because it cannot be modified

D Yes, but only if marked with <code>let</code>

Constants cannot be passed as in-out arguments because they cannot be changed.

What is the main purpose of in-out parameters?

A To allow a function to modify the caller's variable

B To return multiple values from a function

C To make parameters optional

D To improve performance by copying variables

In-out parameters let functions change the original variable passed in.

What error occurs if you forget the & when passing an in-out argument?

A Syntax error

B Compiler error

C Runtime crash

D No error, it works fine

Swift compiler requires the & to clearly show the variable can be modified.

Explain how in-out parameters work in Swift and why they are useful.

Think about how a function can change a variable outside its own scope.

Describe the syntax for declaring and using an in-out parameter in a Swift function.

Focus on the keywords and symbols needed.