错误:类型'String'的值在Swift开关中没有成员'hasSuffix'

Question

我正在关注Swift.org的教程

以下switch语句示例引发错误.

let vegetable = "red pepper"
switch vegetable {
case "celery":
    print("Add some raisins and make ants on a log.")
case "cucumber", "watercress":
    print("That would make a good tea sandwich.")
case let x where x.hasSuffix("pepper"):
    print("Is it a spicy \(x)?")
default:
    print("Everything tastes good in soup.")
}

我得到的错误是: error: value of type 'String' has no member 'hasSuffix' case let x where x.hasSuffix("pepper"): 使用ubuntu 14.04和我的Swift版本swift --version Swift version 3.0 (swift-3.0-PREVIEW-2)

Answer 1

该hasSuffix(_:)成员String来自NSString(并从基金会).在Xcode Playgrounds和项目中使用Swift时,这个方法可以从Swift标准库中获得,而当从例如IBM沙箱/本地Linux机器编译Swift时,Swift std-lib版本是不可访问的,而来自核心的版本-libs基金会是.

要访问后一个实现,您需要显式导入Foundation:

import Foundation // <---

let vegetable = "red pepper"
switch vegetable {
case "celery":
    print("Add some raisins and make ants on a log.")
case "cucumber", "watercress":
    print("That would make a good tea sandwich.")
case let x where x.hasSuffix("pepper"):
    print("Is it a spicy \(x)?")
default:
    print("Everything tastes good in soup.")
}

大多数Swift教程都会假设通过Xcode执行,并且在Xcode之外编译Swift时,import Foundation对于任何"......没有成员......"错误都可以是首次尝试补救.

细节

正如@Hamish在下面的评论中指出的那样(谢谢!),然而hasSuffix(_:),可以从标准库中获得一个实现_runtime(_ObjC).

来自swift/stdlib/public/core/StringLegacy.swift:

#if _runtime(_ObjC)

// ...

public func hasSuffix(_ suffix: String) -> Bool { 
    // ...
}

#else
// FIXME: Implement hasPrefix and hasSuffix without objc
// rdar://problem/18878343
#endif

如果上面的一个不可访问(例如从Linux),则可以使用另一种实现.但是,访问此方法需要隐式import Foundation语句.

来自swift-corelibs-foundation/Foundation/NSString.swift:

#if !(os(OSX) || os(iOS))
extension String {

    // ...

    public func hasSuffix(_ suffix: String) -> Bool {
        // ... core foundation implementation
    }
}
#endif