Interchangeable use of CGFloat and Double types

Paul Hudson      @twostraws

SE-0307 introduced a small but important quality of life improvement: Swift is able to implicitly convert between CGFloat and Double in most places where it is needed.

In its simplest form, this means we can add a CGFloat and a Double together to produce a new Double, like this:

import Foundation
let first: CGFloat = 42
let second: Double = 19
let result = first + second
print(result)

Swift implements this by inserting an implicit initializer as needed, and it will always prefer Double if it’s possible. More importantly, none of this is achieved by rewriting existing APIs: technically things like scaleEffect() in SwiftUI still work with CGFloat, but Swift quietly bridges this to Double.

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Other changes in Swift 5.5…

• Async await
• Async sequences
• Effectful read-only properties
• Structured concurrency
• async let bindings
• Continuations for interfacing async tasks with synchronous code
• Actors
• Global actors
• Sendable and @Sendable closures
• if for postfix member expressions
• Codable synthesis for enums with associated values
• lazy now works in local contexts
• Extending property wrappers to function and closure parameters
• Extending static member lookup in generic contexts

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