ios - 如何在 Swift 中创建 NS_OPTIONS 样式的位掩码枚举？
<p><p>在 Apple 关于与 C API 交互的文档中，他们描述了将 <code>NS_ENUM</code> 标记的 C 样式枚举作为 Swift 枚举导入的方式。这是有道理的，因为 Swift 中的枚举很容易作为 <code>enum</code> 值类型提供，所以很容易看出如何创建我们自己的。</p>
<p>再往下，它说的是关于 <code>NS_OPTIONS</code> 标记的 C 样式选项:</p>
<blockquote>
<p>Swift also imports options marked with the <code>NS_OPTIONS</code> macro. Whereas
options behave similarly to imported enumerations, options can also
support some bitwise operations, such as <code>&</code>, <code>|</code>, and <code>~</code>. In Objective-C,
you represent an empty option set with the constant zero (<code>0</code>). In
Swift, use <code>nil</code> to represent the absence of any options.</p>
</blockquote>
<p>鉴于 Swift 中没有 <code>options</code> 值类型，我们如何创建一个 C-Style options 变量来使用？</p></p>
<br><hr><h1><strong>Best Answer-推荐答案</ strong></h1><br>
<p><h1> swift3.0</h1>
<p>几乎与 Swift 2.0 相同。 OptionSetType 被重命名为 OptionSet 并且枚举按惯例写成小写。</p>
<pre><code>struct MyOptions : OptionSet {
let rawValue: Int
static let firstOption= MyOptions(rawValue: 1 << 0)
static let secondOption = MyOptions(rawValue: 1 << 1)
static let thirdOption= MyOptions(rawValue: 1 << 2)
}
</code></pre>
<p>Swift 3 建议使用空数组文字，而不是提供 <code>none</code> 选项:</p>
<pre><code>let noOptions: MyOptions = []
</code></pre>
<p>其他用法:</p>
<pre><code>let singleOption = MyOptions.firstOption
let multipleOptions: MyOptions = [.firstOption, .secondOption]
if multipleOptions.contains(.secondOption) {
print("multipleOptions has SecondOption")
}
let allOptions = MyOptions(rawValue: 7)
if allOptions.contains(.thirdOption) {
print("allOptions has ThirdOption")
}
</code></pre>
<h1> swift2.0</h1>
<p>在 Swift 2.0 中，协议(protocol)扩展负责处理这些的大部分样板文件，这些样板文件现在作为符合 <code>OptionSetType</code> 的结构导入。 (从 Swift 2 beta 2 开始，<code>RawOptionSetType</code> 已经消失。)声明要简单得多:</p>
<pre><code>struct MyOptions : OptionSetType {
let rawValue: Int
static let None = MyOptions(rawValue: 0)
static let FirstOption= MyOptions(rawValue: 1 << 0)
static let SecondOption = MyOptions(rawValue: 1 << 1)
static let ThirdOption= MyOptions(rawValue: 1 << 2)
}
</code></pre>
<p>现在我们可以通过 <code>MyOptions</code> 使用基于集合的语义:</p>
<pre><code>let singleOption = MyOptions.FirstOption
let multipleOptions: MyOptions = [.FirstOption, .SecondOption]
if multipleOptions.contains(.SecondOption) {
print("multipleOptions has SecondOption")
}
let allOptions = MyOptions(rawValue: 7)
if allOptions.contains(.ThirdOption) {
print("allOptions has ThirdOption")
}
</code></pre>
<h1> swift1.2</h1>
<p>查看由 Swift 导入的 Objective-C 选项(例如 <code>UIViewAutoresizing</code>)，我们可以看到选项被声明为符合协议(protocol)的 <code>struct</code> <code>RawOptionSetType</code>，依次符合<code>_RawOptionSetType</code>、<code>Equatable</code>、<code>RawRepresentable</code>、<code>BitwiseOperationsType</code>、和 <code>NilLiteralConvertible</code>。我们可以像这样创建自己的:</p>
<pre><code>struct MyOptions : RawOptionSetType {
typealias RawValue = UInt
private var value: UInt = 0
init(_ value: UInt) { self.value = value }
init(rawValue value: UInt) { self.value = value }
init(nilLiteral: ()) { self.value = 0 }
static var allZeros: MyOptions { return self(0) }
static func fromMask(raw: UInt) -> MyOptions { return self(raw) }
var rawValue: UInt { return self.value }
static var None: MyOptions { return self(0) }
static var FirstOption: MyOptions { return self(1 << 0) }
static var SecondOption: MyOptions{ return self(1 << 1) }
static var ThirdOption: MyOptions { return self(1 << 2) }
}
</code></pre>
<p>现在我们可以处理这个新的选项集 <code>MyOptions</code>，就像 Apple 文档中描述的那样:您可以使用类似 <code>enum</code> 的语法:</p>
<pre><code>let opt1 = MyOptions.FirstOption
let opt2: MyOptions = .SecondOption
let opt3 = MyOptions(4)
</code></pre>
<p>而且它的行为也像我们期望的选项一样:</p>
<pre><code>let singleOption = MyOptions.FirstOption
let multipleOptions: MyOptions = singleOption | .SecondOption
if multipleOptions & .SecondOption != nil { // see note
println("multipleOptions has SecondOption")
}
let allOptions = MyOptions.fromMask(7) // aka .fromMask(0b111)
if allOptions & .ThirdOption != nil {
println("allOptions has ThirdOption")
}
</code></pre>
<p>我已经建立了一个 <a href="http://natecook.com/blog/2014/07/swift-options-bitmask-generator/" rel="noreferrer noopener nofollow">generator to create a Swift option set</a>没有所有的查找/替换。 </p>
<p><strong>最新:</strong> Swift 1.1 beta 3 的修改。</p></p>
<p style="font-size: 20px;">关于ios - 如何在 Swift 中创建 NS_OPTIONS 样式的位掩码枚举？，我们在Stack Overflow上找到一个类似的问题：
<a href="https://stackoverflow.com/questions/38833030/" rel="noreferrer noopener nofollow" style="color: red;">
https://stackoverflow.com/questions/38833030/
</a>
</p>
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