A microbenchmark for a potential Swift standard library addition

arrays.swift

// 
// FOR FOLKS STUMBLING ACROSS THIS LATER
// This is an example of code that allows us to create arrays by calling a function a fixed number of times.
// In my example below I'm just sending in 5 because I don't want to cloud the benchmark with generating 
// a random number or similar, but with this change you can replace the 5 with `Int.random(in: 1...10)` to
// get an array of random numbers.
//
// HERE'S THE STDLIB ADDITION TO MAKE THIS WORK:
//  @inlinable
//  @_semantics("array.init")
//  public init(builder body: @autoclosure () -> Element, count: Int) {
//    var p: UnsafeMutablePointer<Element>
//    (self, p) = Array._allocateUninitialized(count)
//    for _ in 0..<count {
//      p.initialize(to: body())
//      p += 1
//    }
//  }

import Foundation

let repeatCount = 1000000

for i in 1...10 {
    print("Run \(i):")
    var start = CFAbsoluteTimeGetCurrent()
    let randomNumbers = [Int](builder: 5, count: repeatCount)
    print("New: Generated \(randomNumbers.count) item array in \(CFAbsoluteTimeGetCurrent() - start) seconds")

    start = CFAbsoluteTimeGetCurrent()
    let currentMethod = (1...repeatCount).map { _ in 5 }
    print("Old: Generated \(currentMethod.count) item array in \(CFAbsoluteTimeGetCurrent() - start) seconds")
    print("")
}