具有多个条件的for循环的过滤，关闭，功能语法版本 [英] Filter, Closure, Functional syntax version of for loop with multiple conditions

问题描述

我正在尝试学习一些函数式编程思想，就像Swift中存在的那样.

I'm trying to learn some ideas of functional programming, as they exist in Swift.

在最近的问题中，通过从这里:

var voiceToUse: AVSpeechSynthesisVoice?
let voices = AVSpeechSynthesisVoice.speechVoices()         
for voice in voices {
            if voice.name == "Arthur"
            {
                voiceToUse = voice
            }
        }

对此:

let voiceToUse = AVSpeechSynthesisVoice.speechVoices().filter({ $0.name == "Arthur" }).first

现在，我想知道如何将此技术应用于存在多个条件的问题.可以为此使用这种功能样式吗?

Now I'm wondering how this technique can be applied to a problem where there's multiple criteria. Can this functional style be done to this:

var voiceToUse: AVSpeechSynthesisVoice?
let voices = AVSpeechSynthesisVoice.speechVoices()     
for voice in voices {
                    if voice.name == "Samantha (Enhanced)"  && voice.quality == .enhanced
                    {
                        voiceToUse = voice
                    }
                }

推荐答案

如果要满足条件的数组的第一个元素 用这个.

If you want the first element of the array that satisfies the criteria use this.

if let voiceToUse = AVSpeechSynthesisVoice.speechVoices().first(where: {
        $0.name == "Samantha (Enhanced)" && $0.quality == .enhanced
    }){

      //use the voiceTouse Variable

    }

如果您想要满足以下条件的数组元素的最后一个 条件就用这个.

If you want the last of the element of the array that satisfies the criteria use this.

if let voiceToUse = AVSpeechSynthesisVoice.speechVoices().reversed().first(where: {
       $0.name == "Samantha (Enhanced)" && $0.quality == .enhanced
    }){

      //use the voiceTouse Variable

    }

是的，我们可以使用警卫队...

yes sure, we can use guard let ...

如果不满足一个或多个条件，则使用保护声明将程序控制权移出作用域. 在此示例中，如果不满足条件，即AVSpeechSynthesisVoice.speechVoices()中没有满足条件的元素，则卫兵将把程序控制从检查功能中移出，否则，如果AVSpeechSynthesisVoice中有某些元素.符合条件的speechVoices()，程序的控制权将在卫队let语句之后移至下一行

A guard statement is used to transfer program control out of a scope if one or more conditions aren’t met. in this example, if the condition is not met, ie there is no element in AVSpeechSynthesisVoice.speechVoices() that meet the criteria, guard let will transfer the program control out of the check function ,else if there is the some element in AVSpeechSynthesisVoice.speechVoices() that meet the criteria, program control goes to the next line after the guard let statement

func check(){
guard let voiceToUse =  AVSpeechSynthesisVoice.speechVoices().first(where: {
   $0.name == "Samantha (Enhanced)" && $0.quality == .enhanced
})else{
    return
}
 //use the voiceToUseVariable

}

check()

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