'init' 与 CFStringTransform 和 Swift 3 的模糊使用 [英] Ambiguous use of 'init' with CFStringTransform and Swift 3

问题描述

尝试构建BonMot的示例项目时，

When trying to build the sample project of BonMot,

let theCFMutableString = NSMutableString(string: myString) as CFMutableString
CFStringTransform(theCFMutableString, UnsafeMutablePointer<CFRange>(nil), kCFStringTransformToUnicodeName, false)

我在 CFStringTransform 行上收到此错误

I get this error on the CFStringTransform line

Ambiguous use of 'init' 

Xcode 8 项目使用 Swift 3

The Xcode 8 project uses Swift 3

推荐答案

在 Swift 2 中，指针类型符合 NilLiteralConvertible，允许非可选指针类型表示空指针.因此，当你这样做

In Swift 2, pointer types conformed to NilLiteralConvertible, allowing a non-optional pointer type to represent a null pointer. Therefore when you did

UnsafeMutablePointer<CFRange>(nil)

编译器实际上使用了 UnsafeMutablePointer 的 init(_ other: COpaquePointer) 初始化器，因为 COpaquePointer 是 NilLiteralConvertible，因此可以表示空指针.

the compiler was actually using the init(_ other: COpaquePointer) initialiser of UnsafeMutablePointer, as COpaquePointer is NilLiteralConvertible and can therefore represent a null pointer.

但是在 Swift 3 (SE-0055)，指针类型不再符合 ExpressibleByNilLiteral.现在不再允许非可选指针类型表示空指针，而是使用可选类型来完成，其中 nil 表示空指针.

However in Swift 3 (SE-0055), pointer types no longer conform to ExpressibleByNilLiteral. Rather than allowing a non-optional pointer type to represent a null pointer, this is now simply done with optionals, where nil means a null pointer.

因此，您可以将 nil 直接传递到 CFStringTransform 的 range 参数中，因为它需要一个 UnsafeMutablePointer！:

Therefore you can just pass nil directly into the range parameter of CFStringTransform, as it expects a UnsafeMutablePointer<CFRange>!:

CFStringTransform(theCFMutableString, nil, kCFStringTransformToUnicodeName, false)

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