Swift build time

前言

Swift编译时间过长，是件难以忍受的事情。你能忍心看着几行看似简单的代码，慢吞吞的编译吗？╮(╯_╰)╭。下面来介绍几种减少编译时间的方法。

查看每个函数编译时间

若要对症下药，首先要抓住作祟的小鬼。有2种方法。

1、在build setting中，设置Other Swift Flags为-Xfrontend -debug-time-function-bodies。这样编译时清楚的看到每个函数的编译时间，找到耗时较多的地方。

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点击右边的展开按钮，可详细查看时间。

2.png

2、Xcode plugin，https://github.com/RobertGummesson/BuildTimeAnalyzer-for-Xcode

方法

明确指明类型，不要让编译器去推断

经过测试，发现，在ViewDidLoad中添加如下代码，build的话，在我的机器上一直卡着不动。原因不明，不知道是机器还是xcode问题，还是本身就很慢。但是在原文章说，耗时630ms。总之看起来是比较耗时的。

let myCompany = [
   "employees": [
        "employee 1": ["attribute": "value"],
        "employee 2": ["attribute": "value"],
        "employee 3": ["attribute": "value"],
        "employee 4": ["attribute": "value"],
        "employee 5": ["attribute": "value"],
        "employee 6": ["attribute": "value"],
        "employee 7": ["attribute": "value"],
        "employee 8": ["attribute": "value"],
        "employee 9": ["attribute": "value"],
        "employee 10": ["attribute": "value"],
        "employee 11": ["attribute": "value"],
        "employee 12": ["attribute": "value"],
        "employee 13": ["attribute": "value"],
        "employee 14": ["attribute": "value"],
        "employee 15": ["attribute": "value"],
        "employee 16": ["attribute": "value"],
        "employee 17": ["attribute": "value"],
        "employee 18": ["attribute": "value"],
        "employee 19": ["attribute": "value"],
        "employee 20": ["attribute": "value"],
    ]
]

3.png

但是将类型声明之后，

let myCompany: Dictionary = ...

ViewDidLoad消耗的时间立马降到十几ms。

4.png

nil判断

将nil判断写成if let方式解包。

class CMExpandingTextField: UITextField {

    func textFieldEditingChanged() {
        invalidateIntrinsicContentSize()
    }
    
    override func intrinsicContentSize() -> CGSize {
        if isFirstResponder(), let text = text {
            let size = text.sizeWithAttributes(typingAttributes)
            // Build time: 5238.3ms
            return CGSize(width: size.width + (rightView?.bounds.width ?? 0) + (leftView?.bounds.width ?? 0) + 22, height: bounds.height)
            
  
             // Build time: 32.4ms
        var padding: CGFloat = 22
        if let rightView = rightView {
         padding += rightView.bounds.width
        }

        if let leftView = leftView {
            padding += leftView.bounds.width
        }

        return CGSizeMake(size.width + padding, bounds.height)
        }
        return super.intrinsicContentSize()
    }
}

array+[]

将array+[data]，变成array.append(data)

// Build time: 1250.3ms
let systemOptions = [ 7, 14, 30, -1 ]
let systemNames = (0...2).map{ String(format: localizedFormat, systemOptions[$0]) } + [NSLocalizedString("everything", comment: "")]
// Some code in-between 
labelNames = Array(systemNames[0..

三段式判断 a > b ? a : b

// Build time: 239.0ms
let labelNames = type == 0 ? (1...5).map{type0ToString($0)} : (0...2).map{type1ToString($0)}

// Build time: 16.9ms
var labelNames: [String]
if type == 0 {
    labelNames = (1...5).map{type0ToString($0)}
} else {
    labelNames = (0...2).map{type1ToString($0)}
}

CGFloat-->CGFloat类型转换

// Build time: 3431.7 ms
return CGFloat(M_PI) * (CGFloat((hour + hourDelta + CGFloat(minute + minuteDelta) / 60) * 5) - 15) * unit / 180

// Build time: 3.0ms
return CGFloat(M_PI) * ((hour + hourDelta + (minute + minuteDelta) / 60) * 5 - 15) * unit / 180

Round()

// Build time: 1433.7ms
let expansion = a — b — c + round(d * 0.66) + e
// Build time: 34.7ms
let expansion = a — b — c + d * 0.66 + e

总结

减少编译时间归结于几点：

1、明确指明类型，而不要让编译器去推断代码中你所使用的类型，这样会节省大部分的时间。

2、减少让编译器懵逼的代码，尽量写的简单，明了，不要绕圈子。

Whether or not you have a problem with slow build times, it is still useful to build an understanding of what confuses the compiler. I’m sure you’ll find a few surprises yourself

一句话，要善意的对待编译器，不要整各种来虐待它~ o(￣▽￣)ブ~