字符串插值和字符串连接之间的区别 [英] Difference between String interpolation and String concatenation

问题描述

当专门处理非可选的String值时，字符串插值和字符串串联有什么区别?

When specifically dealing with non-optional String values, what could be the difference between String interpolation and String concatenation?

struct MyModel {
    let value1: String
    let value2: String
    var displayNameByConcatenation: String {
        return value1 + "-" + value2
    }
    var displayNameByInterpolation: String {
        return "\(value1)-\(value2)"
    }
}

• 在任何情况下displayNameByConcatenation和displayNameByInterpolation是不同的吗?像长长的unicode字符串一样?
• 在上面的示例中，是否可以以某种方式覆盖运算符+的行为或插值行为以使其与众不同?
• 一个比另一个快/慢吗?
• Is there going to be any case where displayNameByConcatenation and displayNameByInterpolation are different? Like on long unicode strings?
• Is it possible to somehow override the behavior of operator + or the behavior of interpolation to make them different in above example?
• Is one faster/slower than the other?

请注意，通过此问题，我们可以了解到该字符串插值将使用CustomStringConvertible的description.但是String串联(运算符+)是否也调用description?

Note that from this question we learn that string interpolation will use the description of a CustomStringConvertible. But does String concatenation (operator +) also calls the description?

推荐答案

从速度的角度来看，要区分级联(value1 + "-" + value2)和插值("\(value1)-\(value2)")，结果可能取决于对获取最终的字符串.

From a speed point of view, to differentiate concatenation (value1 + "-" + value2) and interpolation ("\(value1)-\(value2)"), results may depend on the number of operations done to obtain the final string.

我在iPhone 8上的结果显示:

My results on an iPhone 8 show that:

• 如果大约< 30个子字符串连接在一起，则连接速度更快
• 如果大约有30个以上的子字符串要附加在一起，则插值会更快

谢谢塞伦斯(Sirens)弄清楚一个并不一定总是比另一个要快！

Thank you Sirens for figuring out that one wasn't always faster than the other!

亲自尝试一下(不要忘了根据您的需要调整经过测试的字符集和迭代):

Try it yourself (and don't forget to adapt the tested character set and iterations for your needs):

import UIKit

class ViewController: UIViewController {
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        DispatchQueue.global(qos: .default).async {
            ViewController.buildDataAndTest()
        }
    }

    private static func buildDataAndTest(times: Int = 1_000) {
        let characterSet = CharacterSet.alphanumerics
        characterSet.cacheAllCharacters()
        let data: [(String, String)] = (0 ..< times).map { _ in
             (characterSet.randomString(length: 50), characterSet.randomString(length: 20))
        }
        _ = testCIA(data)
        _ = testInterpol(data)
        print("concatenation: " + String(resultConcatenation))
        print("interpolation: \(resultInterpolation)")
    }

    /// concatenation in array
    static var resultConcatenation: CFTimeInterval = 0
    private static func testCIA(_ array: [(String, String)]) -> String {
        var foo = ""
        let start = CACurrentMediaTime()
        for (a, b) in array {
            foo = foo + " " + a + "+" + b
        }
        resultConcatenation = CACurrentMediaTime() - start
        return foo
    }

    /// interpolation
    static var resultInterpolation: CFTimeInterval = 0
    private static func testInterpol(_ array: [(String, String)]) -> String {
        var foo = ""
        let start = CACurrentMediaTime()
        for (a, b) in array {
            foo = "\(foo) \(a)+\(b)"
        }
        resultInterpolation = CACurrentMediaTime() - start
        return foo
    }
}

extension CharacterSet {
    static var cachedCharacters: [Character] = []

    public func cacheAllCharacters() {
        CharacterSet.cachedCharacters = characters()
    }

    /// extracting characters
    /// https://stackoverflow.com/a/52133647/1033581
    public func characters() -> [Character] {
        return codePoints().compactMap { UnicodeScalar($0) }.map { Character($0) }
    }
    public func codePoints() -> [Int] {
        var result: [Int] = []
        var plane = 0
        for (i, w) in bitmapRepresentation.enumerated() {
            let k = i % 8193
            if k == 8192 {
                plane = Int(w) << 13
                continue
            }
            let base = (plane + k) << 3
            for j in 0 ..< 8 where w & 1 << j != 0 {
                result.append(base + j)
            }
        }
        return result
    }

    // http://stackoverflow.com/a/42895178/1033581
    public func randomString(length: Int) -> String {
        let charArray = CharacterSet.cachedCharacters
        let charArrayCount = UInt32(charArray.count)
        var randomString = ""
        for _ in 0 ..< length {
            randomString += String(charArray[Int(arc4random_uniform(charArrayCount))])
        }
        return randomString
    }
}

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