以下是我previous post on Swift optionals后的问题的详细说明。
感谢给定here, here和here的潜在客户,我能够读取分数(代表谐波比率)或小数( for cents) )从字符串数组中计算音阶中音符的频率。
首先测试字符串数组中的每个元素,看它是否包含/
或.
两个函数中的一个然后使用可选链接识别输入错误,因此小数和小数都符合规则在tuning file format中概述。
示例1和1a显示了以两种格式正确输入数据时会发生什么。
使用分数和小数的混合来缩放
C D E F G Ab B C’
let tuning = [ "1/1", "193.15686", "5/4", "503.42157", "696.57843", "25/16", "1082.89214", "2/1"]
调试区域中的列显示输入数据(自上而下),行显示输出频率(l-to-r)。
Optional("1/1")
Optional("193.15686")
Optional("5/4")
Optional("503.42157")
Optional("696.57843")
Optional("25/16")
Optional("1082.89214")
Optional("2/1")
[261.62599999999998, 292.50676085897425, 327.03249999999997, 349.91970174951047, 391.22212058238728, 408.79062499999998, 489.02764963627084, 523.25199999999995]
示例2&图3显示了两个函数如何对坏输入作出反应(即错误输入的数据)。
报告的坏分数(例如,缺失的分母打印消息)
Optional("1/1")
Optional("5/")
User input error - invalid fraction: frequency now being set to 0.0 Hertz
Optional("500.0")
Optional("700.0")
Optional("2/1")
[261.62599999999998, 0.0, 349.22881168708938, 391.99608729493866, 523.25199999999995]
不报告的错误小数(例如700之后没有.0 - 这应该会产生一条消息)
Optional("1/1")
Optional("5/4")
Optional("500.0")
Optional("700")
Optional("2/1")
[261.62599999999998, 327.03249999999997, 349.22881168708938, 0.0, 523.25199999999995]
注意:除了报告,当可选项为零时,行中会显示0.0(Hz)。这被插入到代码的其他地方(,在上下文中用注释进行解释。)
问题简而言之?分数函数报告故障,而十进制数函数未能检测到错误输入。
两个函数都使用带有guard语句的可选链接。这适用于错误的分数,但我没有做任何事情会使函数报告小数的错误输入条件。在彻底检查了代码后,我确信问题在于我为守卫声明设定的条件。但我无法做到这一点。谁能解释一下我做错了什么?
Tuner.swift
import UIKit
class Tuner {
var tuning = [String]()
let tonic: Double = 261.626 // frequency of middle C
var index = -1
let centsPerOctave: Double = 1200.0 // mandated by Scala tuning file format
let formalOctave: Double = 2.0 // Double for stretched-octave tunings
init(tuning: [String]) {
self.tuning = tuning
let frequency = tuning.flatMap(doubleFromDecimalOrFraction)
print(frequency)
}
func doubleFromDecimalOrFraction(s: String?) -> Double {
index += 1
let whichNumericStringType = s
print(whichNumericStringType as Any) // eavesdrop on String?
var possibleFrequency: Double?
// first process decimal.
if (whichNumericStringType?.contains("."))! {
possibleFrequency = processDecimal(s: s)
}
// then process fractional.
if (whichNumericStringType?.contains("/"))! {
possibleFrequency = processFractional(s: s)
}
// Insert "0.0" marker. Remove when processDecimal works
let noteFrequency = possibleFrequency
let zeroFrequency = 0.0
// when noteFrequency? is nil, possibleFrequency is set to zeroFrequency
let frequency = noteFrequency ?? zeroFrequency
return frequency // TO DO let note: (index: Int, frequency: Double)
}
func processFractional(s: String?) -> Double? {
var fractionArray = s?.components(separatedBy: "/")
guard let numerator = Double((fractionArray?[0])!.digits),
let denominator = Double((fractionArray?[1])!.digits),
numerator > 0,
denominator != 0,
fractionArray?.count == 2
else
{
let possibleFrequency = 0.0
print("User input error - invalid fraction: frequency now being set to \(possibleFrequency) Hertz ")
return possibleFrequency
}
let possibleFrequency = tonic * (numerator / denominator)
return possibleFrequency
}
func processDecimal(s: String?) -> Double? {
let decimalArray = s?.components(separatedBy: ".")
guard let _ = s,
decimalArray?.count == 2
else
{
let denominator = 1
let possibleFrequency = 0.0
print("User input error (value read as \(s!.digits)/\(denominator) - see SCL format, http://www.huygens-fokker.org/scala/scl_format.html): frequency now being forced to \(possibleFrequency) Hertz ")
return possibleFrequency
}
let power = Double(s!)!/centsPerOctave
let possibleFrequency = tonic * (formalOctave**power)
return possibleFrequency
}
}
extension String {
var digits: String {
return components(separatedBy: CharacterSet.decimalDigits.inverted).joined()
}
}
precedencegroup Exponentiative {
associativity: left
higherThan: MultiplicationPrecedence
}
infix operator ** : Exponentiative
func ** (num: Double, power: Double) -> Double{
return pow(num, power)
}
ViewController.swift
import UIKit
class ViewController: UIViewController {
// test pitches: rational fractions and decimal numbers (currently 'good')
let tuning = ["1/1", "5/4", "500.0", "700.0", "2/1"]
// Diatonic scale: rational fractions
// let tuning = [ "1/1", "9/8", "5/4", "4/3", "3/2", "27/16", "15/8", "2/1"]
// Mohajira: rational fractions
// let tuning = [ "21/20", "9/8", "6/5", "49/40", "4/3", "7/5", "3/2", "8/5", "49/30", "9/5", "11/6", "2/1"]
// Diatonic scale: 12-tET
// let tuning = [ "0.0", "200.0", "400.0", "500", "700.0", "900.0", "1100.0", "1200.0"]
// Diatonic scale: mixed 12-tET and rational fractions
// let tuning = [ "0.0", "9/8", "400.0", "4/3", "700.0", "27/16", "1100.0", "2/1"]
// Diatonic scale: 19-tET
// let tuning = [ "0.0", "189.48", "315.8", "505.28", "694.76", "884.24", "1073.72", "1200.0"]
// Diatonic 1/4-comma meantone scale. Pietro Aaron's temperament (1523) : mixed cents and rational fractions
// let tuning = [ "1/1", "193.15686", "5/4", "503.42157", "696.57843", "25/16", "1082.89214", "2/1"]
override func viewDidLoad() {
super.viewDidLoad()
_ = Tuner(tuning: tuning)
}
}
答案 0 :(得分:3)
问题简而言之?分数函数报告错误,而十进制数函数无法检测错误输入。
十进制数函数确实检测到“错误”输入。但是,"700"
不包含"."
,如果字符串包含processDecimal(s:)
,则只调用"."
。如果字符串不包含"."
且不包含"/"
,则doubleFromDecimalOrFraction(s:)
不会调用任何函数来解析字符串。