弦乐演奏

稍微讲讲性能 UI测试包在iPhone 7(真实设备)与iOS 14

let i = 0
lt result1 = String(i) //0.56s 5890kB
lt result2 = "\(i)" //0.624s 5900kB
lt result3 = i.description //0.758s 5890kB

import XCTest

class ConvertIntToStringTests: XCTestCase {
    let count = 1_000_000
    
    func measureFunction(_ block: () -> Void) {
        let metrics: [XCTMetric] = [
            XCTClockMetric(),
            XCTMemoryMetric()
        ]
        let measureOptions = XCTMeasureOptions.default
        measureOptions.iterationCount = 5
        
        measure(metrics: metrics, options: measureOptions) {
            block()
        }
    }

    func testIntToStringConstructor() {
        var result = ""
        measureFunction {
            for i in 0...count {
                result += String(i)
            }
        }
    }
    
    func testIntToStringInterpolation() {
        var result = ""
        measureFunction {
            for i in 0...count {
                result += "\(i)"
            }
        }
    }
    
    func testIntToStringDescription() {
        var result = ""
        measureFunction {
            for i in 0...count {
                result += i.description
            }
        }
    }
}

斯威夫特4:

试图在label中显示没有Optional()字的值。

这里x是一个Int值使用。

let str:String = String(x ?? 0)

斯威夫特2:

var num1 = 4
var numString = "56"
var sum2 = String(num1) + numString
var sum3 = Int(numString)

let intAsString = 45.description     // "45"
let stringAsInt = Int("45")          // 45

斯威夫特4:

let x:Int = 45
let str:String = String(describing: x)

开发者。Apple.com >字符集init(describing:)

String(description:)初始化式是将任何类型的实例转换为字符串的首选方法。

自定义字符串转换

let Str = "12"
let num: Int = 0
num = Int (str)