Generic subscripts in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a generic subscript in Swift?

A generic subscript allows you to define a subscript that can work with any type, using a placeholder type parameter. This makes the subscript flexible and reusable for different data types.

beginner

How do you declare a generic subscript in Swift?

You declare a generic subscript by adding a generic type parameter in angle brackets <> after the subscript keyword, like: <br>subscript<T>(index: Int) -> T { ... }

intermediate

Why use generic subscripts instead of regular subscripts?

Generic subscripts let you write one subscript that works with many types, reducing code duplication and increasing flexibility. Regular subscripts work with fixed types only.

intermediate

Can a generic subscript have multiple generic parameters?

Yes, a generic subscript can have multiple generic parameters, just like generic functions. For example: <br>subscript(key: T) -> U { ... }

beginner

Give a simple example of a generic subscript in Swift.

Example:<br><code>struct Box {<br>  private var items = [Any]()<br>  subscript<T>(index: Int) -> T? {<br>    get { items[index] as? T }<br>    set { if let newValue = newValue { items[index] = newValue } }<br>  }<br>}</code><br>This subscript can get or set items of any type safely.

What does the <T> mean in a generic subscript declaration in Swift?

A It limits the subscript to only Int types.

B It declares a placeholder type that can be any type.

C It specifies the subscript returns a tuple.

D It is a syntax error in Swift.

The declares a generic type parameter, meaning the subscript can work with any type T.

Can a generic subscript return different types depending on the caller?

A Yes, the caller decides the type by specifying it.

B No, the return type is fixed.

C Only if the subscript is static.

D Only if the subscript uses Int as generic type.

Generic subscripts can return different types because the caller specifies the type when using the subscript.

Which keyword is used to define a subscript in Swift?

A func

B index

C subscript

D get

The keyword 'subscript' defines a subscript in Swift.

Is it possible to have a generic subscript with constraints on the generic type?

A Yes, you can add constraints like <T: Equatable>.

B No, generic subscripts cannot have constraints.

C Only for classes, not structs.

D Only if the subscript is private.

Generic subscripts can have constraints on their generic types, just like generic functions.

What happens if you try to access a generic subscript with a type that does not match the stored data?

A It causes a compile-time error.

B It automatically converts the type.

C It always returns a default value.

D It returns nil if optional or causes a runtime error.

If the type does not match, optional generic subscripts return nil; otherwise, it may cause a runtime error.

Explain what a generic subscript is and why it is useful in Swift.

Think about how generics help functions work with many types.

Write a simple Swift struct with a generic subscript that stores and retrieves values of any type.

Use an array of Any and cast inside the subscript.