Understanding Swift’s Opaque Types

Useful for SwiftUI

Steven Curtis
4 min readSep 21, 2022


Photo by Rod Long on Unsplash

Before we start

Difficulty: Beginner | Easy | Normal | Challenging

This article has been developed using Xcode 12.2, and Swift 5.3


* You will be expected to be aware how to make a Single View Application in Swift, or be able to use Playgrounds to be able to code in Swift

* I lean rather heavily on Generics

* Access Control is briefly touched upon

* Some knowledge of Protocols would be useful

* Equatable is used later in the article

Keywords and Terminology

Opaque Types: A data type whose concrete data structure is not defined in an interface

This project


SwiftUI makes use of the some keyword, as

The (rather simplistic) explanation is that the some keyword indicates that the body property has an opaque type, that is obstruficating type information contained in the body (we can think of the type information as being private). body represents a class that implements View. You need a concrete object for the View, but it doesn’t matter which View is used rather the capabilities of some View are needed.

The Idea of a Reverse Generic type

Generic types let the code that calls a function type for that function’s parameters and return a value in a way this is abstracted from the function implementation.

Let us look at the following Generic