对于协议，要求实例变量符合协议；而不是有一个特定的类型

发布于 2025-01-12 23:15:33 字数 998 浏览 2 评论 0原文

作为自定义 Coder 的一部分，我以完全相同的方式转换 Float 和 Double ：

static func encode(_ value : Double) -> Data {
    withUnsafeBytes(of: value.bitPattern.bigEndian) { Data($0) }
}

static func encode(_ value : Float) -> Data {
    withUnsafeBytes(of: value.bitPattern.bigEndian) { Data($0) }
}

我认为我可以要求 >value 将符合协议，并且由于 FloatingPoint 协议不保证 bitPattern 的存在，我想我会自己制作：

protocol CompatibleFloatingPoint {
    var bitPattern : FixedWidthInteger { get }
}

但是，给出以下错误： 协议“FixedWidthInteger”只能用作通用约束，因为它具有 Self 或关联的类型要求

但是，我无法将 FixedWidthInteger 替换为特定类型，如 Double .bitPattern 是 UInt64 ，而 Float.bitPattern 是 UInt32

正确的语法是什么要求 bitPattern 符合 FixedWidthInteger 协议而不强制其具有特定类型？

原文

As part of a custom Coder, I convert both Float and Double in the exact same way :

static func encode(_ value : Double) -> Data {
    withUnsafeBytes(of: value.bitPattern.bigEndian) { Data($0) }
}

static func encode(_ value : Float) -> Data {
    withUnsafeBytes(of: value.bitPattern.bigEndian) { Data($0) }
}

I thought that instead I could require that value would conform to a protocol, and since the FloatingPoint protocol does not guarantee the presence of bitPattern, I thought I would make my own :

protocol CompatibleFloatingPoint {
    var bitPattern : FixedWidthInteger { get }
}

This, however, gives the following error :
Protocol 'FixedWidthInteger' can only be used as a generic constraint because it has Self or associated type requirements

However, I cannot replace FixedWidthInteger with a specific type, as Double.bitPattern is a UInt64 and Float.bitPattern is a UInt32

What is the proper syntax to require that bitPattern conform to the FixedWidthInteger protocol without forcing it to have a specific type ?

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听风吹 2025-01-19 23:15:33

您正在寻找的是关联类型。这正是您所描述的内容（所需的类型符合协议，而不是该协议的存在）：

protocol CompatibleFloatingPoint {
    associatedtype BitPattern: FixedWidthInteger
    var bitPattern : BitPattern { get }
}

extension Float: CompatibleFloatingPoint {}
extension Double: CompatibleFloatingPoint {}

有关更多详细信息，请参阅 Swift 编程语言中的关联类型。

What you're looking for is an associated type. This means exactly what you've described (the required type conforms to a protocol rather than being the existential of that protocol):

protocol CompatibleFloatingPoint {
    associatedtype BitPattern: FixedWidthInteger
    var bitPattern : BitPattern { get }
}

extension Float: CompatibleFloatingPoint {}
extension Double: CompatibleFloatingPoint {}

For more details, see Associated Types in the Swift Programming Language.

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