快速连接字符串

关于性能的几句话

UI测试包在iPhone 7(真实设备)，iOS 14， -Onone(调试，没有优化)[关于]

var result = ""
for i in 0...count {
    <concat_operation>
}

计数= 5_000

//Append
result.append(String(i))                         //0.007s 39.322kB

//Plus Equal
result += String(i)                              //0.006s 19.661kB

//Plus
result = result + String(i)                      //0.130s 36.045kB

//Interpolation
result = "\(result)\(i)"                         //0.164s 16.384kB

//NSString
result = NSString(format: "%@%i", result, i)     //0.354s 108.142kB

//NSMutableString
result.append(String(i))                         //0.008s 19.661kB

禁用下一个测试:

加上高达100_000 ~10s 插补可达100_000 ~10s NSString高达10_000 ->内存问题

Count = 1_000_000

//Append
result.append(String(i))                         //0.566s 5894.979kB

//Plus Equal
result += String(i)                              //0.570s 5894.979kB

//NSMutableString
result.append(String(i))                         //0.751s 5891.694kB

*注意将Int转换为字符串

源代码

import XCTest

class StringTests: XCTestCase {
    let count = 1_000_000
    
    let metrics: [XCTMetric] = [
        XCTClockMetric(),
        XCTMemoryMetric()
    ]
    
    let measureOptions = XCTMeasureOptions.default
    
    override func setUp() {
        measureOptions.iterationCount = 5
    }
    
    func testAppend() {
        var result = ""
        measure(metrics: metrics, options: measureOptions) {
            for i in 0...count {
                result.append(String(i))
            }
        }
    }
    
    func testPlusEqual() {
        var result = ""
        measure(metrics: metrics, options: measureOptions) {
            for i in 0...count {
                result += String(i)
            }
        }
    }
    
    func testPlus() {
        var result = ""
        measure(metrics: metrics, options: measureOptions) {
            for i in 0...count {
                result = result + String(i)
            }
        }
    }
    
    func testInterpolation() {
        var result = ""
        measure(metrics: metrics, options: measureOptions) {
            for i in 0...count {
                result = "\(result)\(i)"
            }
        }
    }
    
    //Up to 10_000
    func testNSString() {
        var result: NSString =  ""
        measure(metrics: metrics, options: measureOptions) {
            for i in 0...count {
                result = NSString(format: "%@%i", result, i)
            }
        }
    }
    
    func testNSMutableString() {
        let result = NSMutableString()
        measure(metrics: metrics, options: measureOptions) {
            for i in 0...count {
                result.append(String(i))
            }
        }
    }
}

let the_string = "Swift"
let resultString = "\(the_string) is a new Programming Language"

你现在可以在Swift中使用stringByAppendingString。

var string = "Swift"
var resultString = string.stringByAppendingString(" is new Programming Language")

它被称为字符串插值。 它是用常量，变量，字面量和表达式创建新字符串的方法。 例子:

      let price = 3
      let staringValue = "The price of \(price) mangoes is equal to \(price*price) "

也

let string1 = "anil"
let string2 = "gupta"
let fullName = string1 + string2  // fullName is equal to "anilgupta"
or 
let fullName = "\(string1)\(string2)" // fullName is equal to "anilgupta"

它也意味着串联字符串值。

希望这对你有所帮助。

你可以使用SwiftString (https://github.com/amayne/SwiftString)来做这件事。

"".join(["string1", "string2", "string3"]) // "string1string2string"
" ".join(["hello", "world"]) // "hello world"

免责声明:我写了这个扩展

我刚从Objective-C切换到Swift(4)，我发现我经常使用:

let allWords = String(format:"%@ %@ %@",message.body!, message.subject!, message.senderName!)