ReadmeExample.swift

import Benchmark
import Foundation
import Parsing

/// This benchmark measures the performance of the examples given in the library's README.
let readmeExampleSuite = BenchmarkSuite(name: "README Example") { suite in
  #if swift(>=5.8)
    let input = """
      1,Blob,true
      2,Blob Jr.,false
      3,Blob Sr.,true
      """
    let expectedOutput = [
      User(id: 1, name: "Blob", isAdmin: true),
      User(id: 2, name: "Blob Jr.", isAdmin: false),
      User(id: 3, name: "Blob Sr.", isAdmin: true),
    ]
    var output: [User]!

    struct User: Equatable {
      var id: Int
      var name: String
      var isAdmin: Bool
    }

    do {
      struct UserParser: Parser {
        var body: some Parser<Substring, User> {
          Parse(User.init(id:name:isAdmin:)) {
            Int.parser()
            ","
            Prefix { $0 != "," }.map(String.init)
            ","
            Bool.parser()
          }
        }
      }

      struct UsersParser: Parser {
        var body: some Parser<Substring, [User]> {
          Many {
            UserParser()
          } separator: {
            "\n"
          } terminator: {
            End()
          }
        }
      }

      let users = UsersParser()
      suite.benchmark("Parser: Substring") {
        var input = input[...]
        output = try users.parse(&input)
      } tearDown: {
        precondition(output == expectedOutput)
      }
    }

    do {
      struct UserParser: Parser {
        var body: some Parser<Substring.UTF8View, User> {
          Parse(User.init(id:name:isAdmin:)) {
            Int.parser()
            ",".utf8
            Prefix { $0 != UInt8(ascii: ",") }.map { String(Substring($0)) }
            ",".utf8
            Bool.parser()
          }
        }
      }

      struct UsersParser: Parser {
        var body: some Parser<Substring.UTF8View, [User]> {
          Many {
            UserParser()
          } separator: {
            "\n".utf8
          } terminator: {
            End()
          }
        }
      }

      let users = UsersParser()
      suite.benchmark("Parser: UTF8") {
        var input = input[...].utf8
        output = try users.parse(&input)
      } tearDown: {
        precondition(output == expectedOutput)
      }
    }

    suite.benchmark("Ad hoc") {
      output =
        input
        .split(separator: "\n")
        .compactMap { row -> User? in
          let fields = row.split(separator: ",")
          guard
            fields.count == 3,
            let id = Int(fields[0]),
            let isAdmin = Bool(String(fields[2]))
          else { return nil }

          return User(id: id, name: String(fields[1]), isAdmin: isAdmin)
        }
    } tearDown: {
      precondition(output == expectedOutput)
    }

    if #available(macOS 10.15, *) {
      let scanner = Scanner(string: input)
      suite.benchmark("Scanner") {
        output = []
        while scanner.currentIndex != input.endIndex {
          guard
            let id = scanner.scanInt(),
            let _ = scanner.scanString(","),
            let name = scanner.scanUpToString(","),
            let _ = scanner.scanString(","),
            let isAdmin = scanner.scanBool()
          else { break }

          output.append(User(id: id, name: name, isAdmin: isAdmin))
          _ = scanner.scanString("\n")
        }
      } setUp: {
        scanner.currentIndex = input.startIndex
      } tearDown: {
        precondition(output == expectedOutput)
      }
    }
  #endif
}