Related
Code:
extension Array {
// Total Together An Array
func FindTotal(_ arrayName: [Int]) -> Int {
var currentValue: Int = 0
for i in 0...Int(arrayName.count - 1) {
currentValue = currentValue + Int(arrayName[i])
}
return currentValue
}
// Number Grabber for Calculating the values
func calcItemsD(_ TargetArray: [String]) {
var placeholder: String? = nil
for i in 0...Int(TargetArray.count - 1) {
placeholder = String((TargetArray[i]).character(at: 0)!)
if (placeholder == "1") {
dealerNums.append("")
}
}
}
}
class DeckSetup : ObservableObject {
#Published public var deckOCards: [String] = []
#Published public var yourhand: [String] = []
#Published public var dealerHand: [String] = []
#Published public var dealerNums: [Int] = [7, 2]
#Published public var playerNums: [Int] = []
}
The dealerNums.append("") is throwing the error of out of scope and I am not sure why Heres the all the code that should be relevant.
dealerNums is an array encapsulated in your DeckSetup class. You can't access that from an Array extension.
What you can do, is pass in dealerNums into the function, like so:
func calcItemsD(_ targetArray: [String], dealerNums: inout [Int]) {
var placeholder: String? = nil
for i in 0 ..< targetArray.count {
placeholder = String(targetArray[i].first!)
if placeholder == "1" {
dealerNums.append("")
}
}
}
And called like so from inside your DeckSetup class:
calcItemsD(["1", "K", "A"], dealerNums: &dealerNums)
dealerNums is marked inout, since you are mutating it within the function.
I cleaned up the function a tiny bit, but I don't know if you have more to it. For example, these are more things you could change to improve it:
Iterate with for target in targetArray instead of using the index.
placeholder is not needed to be stored outside the loop as it isn't used. You can have a local let placeholder = ... if needed.
Don't force unwrap (!) the first character. Provide a suitable alternative or fallback.
I am using an array that is filled with structs:
struct CartModel: Codable {
var product_id: Int
var line_subtotal: Float
var line_total: Float
var line_tax: Float
var line_subtotal_tax: Float
var key: String
var quantity: Int
}
static var fullCart = [CartModel]()
Now I am trying to delete one of those from the array.
I tried to use fullCart.index(of:), but it is giving me the following error:
Argument labels '(of:, _:)' do not match any available overloads
I was hoping to use fullCart.remove(at:), but because of not being able to find the right index I am not sure how to remove the right item.
You also can find index by index(where:) and then delete item from array:
if let index = fullCart.index(where: { $0.product_id == otherCartModel.product_id }) {
fullCart.remove(at: index)
}
Or conform to Equatable protocol and use index(of:):
struct CartModel: Codable, Equatable {
...
static func == (lhs: Self, rhs: Self) -> Bool {
return lhs.product_id == rhs.product_id
}
}
if let index = fullCart.index(of: otherCartModel) {
fullCart.remove(at: index)
}
I already have several arrays for strings. I want to add them to a list of arrays, so I can use a predefined (enum) index. The individual arrays are already in place, I only need to access them via index (fixed with enum or within a loop with index from enum type). So there should be no copy of the strings within the array, only a reference to the array itself.
I already have this in mind:
enum TypeOfArray: Int {
case Src = 0, Dest, SrcCache, DstCache, N
}
var srcFolders : [String] = []
var dstFolders : [String] = []
var srcFoldersCache : [String] = []
var dstFoldersCache : [String] = []
var allFolders: [[String]] = []
Then I want to initilaze the main array by assigning each of the individual arrays. But this is rejected by the compiler: ("Cannot subscript a value of type '[[String]]' with an index of type 'TypeArray'")
allFolders[TypeOfArray.Src] = srcFolders
I don't know if this "typesave" index is even possible.
Can I use a fixed index range 0..N when defining for optimizing memory or speed?
Any ideas?
A dictionary would be a good solution for this:
var dict = [TypeOfArray:[String]]()
dict[TypeOfArray.Src] = srcFolders
Singleton
If you want to share the content of your arrays, an you want the updates to be reflected in your code, you can use a Singleton
final class ImageNameManager {
static let sharedInstance = ImageNameManager()
var srcFolders: [String]
var dstFolders: [String]
var srcFoldersCache: [String]
var dstFoldersCache: [String]
private init() {
// populate: srcFolders, dstFolders, srcFoldersCache, dstFoldersCache
srcFolders = []
dstFolders = []
srcFoldersCache = []
dstFoldersCache = []
}
enum ImageType: Int {
case Src = 0, Dest, SrcCache, DstCache
}
func imageNames(imageType: ImageType) -> [String] {
switch imageType {
case .Src: return srcFolders
case .Dest: return dstFolders
case .SrcCache: return srcFoldersCache
case .DstCache: return dstFoldersCache
}
}
}
Usage
Now you can populate one of your array
ImageNameManager.sharedInstance.dstFolders.append("Hello")
and receives the new data in another section of your code
let dstFolders = ImageNameManager.sharedInstance.imageNames(.Dest)
// ["Hello"]
Update
In order to share the same array across your app you cal also use this code
final class ImageNameManager {
static let sharedInstance = ImageNameManager()
var srcFolders: [String] = []
var dstFolders: [String] = []
var srcFoldersCache: [String] = []
var dstFoldersCache: [String] = []
}
Now alway reference it the array with this code ImageNameManager.sharedInstance.dstFolders, look
ImageNameManager.sharedInstance.dstFolders.append("Hello")
ImageNameManager.sharedInstance.dstFolders.append("World")
ImageNameManager.sharedInstance.dstFolders // ["Hello", "World"]
How can I extend Swift's Array<T> or T[] type with custom functional utils?
Browsing around Swift's API docs shows that Array methods are an extension of the T[], e.g:
extension T[] : ArrayType {
//...
init()
var count: Int { get }
var capacity: Int { get }
var isEmpty: Bool { get }
func copy() -> T[]
}
When copying and pasting the same source and trying any variations like:
extension T[] : ArrayType {
func foo(){}
}
extension T[] {
func foo(){}
}
It fails to build with the error:
Nominal type T[] can't be extended
Using the full type definition fails with Use of undefined type 'T', i.e:
extension Array<T> {
func foo(){}
}
And it also fails with Array<T : Any> and Array<String>.
Curiously Swift lets me extend an untyped array with:
extension Array {
func each(fn: (Any) -> ()) {
for i in self {
fn(i)
}
}
}
Which it lets me call with:
[1,2,3].each(println)
But I can't create a proper generic type extension as the type seems to be lost when it flows through the method, e.g trying to replace Swift's built-in filter with:
extension Array {
func find<T>(fn: (T) -> Bool) -> T[] {
var to = T[]()
for x in self {
let t = x as T
if fn(t) {
to += t
}
}
return to
}
}
But the compiler treats it as untyped where it still allows calling the extension with:
["A","B","C"].find { $0 > "A" }
And when stepped-thru with a debugger indicates the type is Swift.String but it's a build error to try access it like a String without casting it to String first, i.e:
["A","B","C"].find { ($0 as String).compare("A") > 0 }
Does anyone know what's the proper way to create a typed extension method that acts like the built-in extensions?
For extending typed arrays with classes, the below works for me (Swift 2.2). For example, sorting a typed array:
class HighScoreEntry {
let score:Int
}
extension Array where Element == HighScoreEntry {
func sort() -> [HighScoreEntry] {
return sort { $0.score < $1.score }
}
}
Trying to do this with a struct or typealias will give an error:
Type 'Element' constrained to a non-protocol type 'HighScoreEntry'
Update:
To extend typed arrays with non-classes use the following approach:
typealias HighScoreEntry = (Int)
extension SequenceType where Generator.Element == HighScoreEntry {
func sort() -> [HighScoreEntry] {
return sort { $0 < $1 }
}
}
In Swift 3 some types have been renamed:
extension Sequence where Iterator.Element == HighScoreEntry
{
// ...
}
After a while trying different things the solution seems to remove the <T> from the signature like:
extension Array {
func find(fn: (T) -> Bool) -> [T] {
var to = [T]()
for x in self {
let t = x as T;
if fn(t) {
to += t
}
}
return to
}
}
Which now works as intended without build errors:
["A","B","C"].find { $0.compare("A") > 0 }
Extend all types:
extension Array where Element: Any {
// ...
}
Extend Comparable types:
extension Array where Element: Comparable {
// ...
}
Extend some types:
extension Array where Element: Comparable & Hashable {
// ...
}
Extend a particular type:
extension Array where Element == Int {
// ...
}
I had a similar problem - wanted to extend the general Array with a swap() method, which was supposed to take an argument of the same type as the array. But how do you specify the generic type? I found by trial and error that the below worked:
extension Array {
mutating func swap(x:[Element]) {
self.removeAll()
self.appendContentsOf(x)
}
}
The key to it was the word 'Element'. Note that I didn't define this type anywhere, it seems automatically exist within the context of the array extension, and refer to whatever the type of the array's elements is.
I am not 100% sure what's going on there, but I think it is probably because 'Element' is an associated type of the Array (see 'Associated Types' here https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Generics.html#//apple_ref/doc/uid/TP40014097-CH26-ID189)
However, I can't see any reference of this in the Array structure reference (https://developer.apple.com/library/prerelease/ios/documentation/Swift/Reference/Swift_Array_Structure/index.html#//apple_ref/swift/struct/s:Sa)... so I'm still a little unsure.
Using Swift 2.2:
I ran into a similar issue when trying to remove duplicates from an array of strings. I was able to add an extension on the Array class that does just what I was looking to do.
extension Array where Element: Hashable {
/**
* Remove duplicate elements from an array
*
* - returns: A new array without duplicates
*/
func removeDuplicates() -> [Element] {
var result: [Element] = []
for value in self {
if !result.contains(value) {
result.append(value)
}
}
return result
}
/**
* Remove duplicate elements from an array
*/
mutating func removeDuplicatesInPlace() {
var result: [Element] = []
for value in self {
if !result.contains(value) {
result.append(value)
}
}
self = result
}
}
Adding these two methods to the Array class allows me to call one of the two methods on an array and successfully remove duplicates. Note that the elements in the array must conform to the Hashable protocol. Now I can do this:
var dupes = ["one", "two", "two", "three"]
let deDuped = dupes.removeDuplicates()
dupes.removeDuplicatesInPlace()
// result: ["one", "two", "three"]
If you want to learn about extending Arrays and other types of build in classes checkout code in this github repo https://github.com/ankurp/Cent
As of Xcode 6.1 the syntax to extend arrays is as follows
extension Array {
func at(indexes: Int...) -> [Element] {
... // You code goes herer
}
}
I had a look at the Swift 2 standard library headers, and here is the prototype for the filter function, which makes it quite obvious how to roll your own.
extension CollectionType {
func filter(#noescape includeElement: (Self.Generator.Element) -> Bool) -> [Self.Generator.Element]
}
It's not an extension to Array, but to CollectionType, so the same method applies to other collection types. #noescape means that the block passed in will not leave the scope of the filter function, which enables some optimisations. Self with a capital S is the class we are extending. Self.Generator is an iterator that iterates through the objects in the collection and Self.Generator.Element is the type of the objects, for example for an array [Int?] Self.Generator.Element would be Int?.
All in all this filter method can be applied to any CollectionType, it needs a filter block which takes an element of the collection and returns a Bool, and it returns an array of the original type. So putting this together, here's a method that I find useful: It combines map and filter, by taking a block that maps a collection element to an optional value, and returns an array of those optional values that are not nil.
extension CollectionType {
func mapfilter<T>(#noescape transform: (Self.Generator.Element) -> T?) -> [T] {
var result: [T] = []
for x in self {
if let t = transform (x) {
result.append (t)
}
}
return result
}
}
import Foundation
extension Array {
var randomItem: Element? {
let idx = Int(arc4random_uniform(UInt32(self.count)))
return self.isEmpty ? nil : self[idx]
}
}
(Swift 2.x)
You can also extend the array to conform to a protocol containing blue-rpints for generic type methods, e.g., a protocol containing your custom functional utils for all generic array elements conforming to some type constraint, say protocol MyTypes. The bonus using this approach is that you can write functions taking generic array arguments, with a constraint that these array arguments must conform to your custom function utilities protocol, say protocol MyFunctionalUtils.
You can get this behaviour either implicitly, by type constraining the array elements to MyTypes, or---as I will show in the method I describe below---, quite neatly, explicitly, letting your generic array functions header directly show that input arrays conforms to MyFunctionalUtils.
We begin with Protocols MyTypes for use as type constraint; extend the types you want to fit in your generics by this protocol (example below extends fundamental types Int and Double as well as a custom type MyCustomType)
/* Used as type constraint for Generator.Element */
protocol MyTypes {
var intValue: Int { get }
init(_ value: Int)
func *(lhs: Self, rhs: Self) -> Self
func +=(inout lhs: Self, rhs: Self)
}
extension Int : MyTypes { var intValue: Int { return self } }
extension Double : MyTypes { var intValue: Int { return Int(self) } }
// ...
/* Custom type conforming to MyTypes type constraint */
struct MyCustomType : MyTypes {
var myInt : Int? = 0
var intValue: Int {
return myInt ?? 0
}
init(_ value: Int) {
myInt = value
}
}
func *(lhs: MyCustomType, rhs: MyCustomType) -> MyCustomType {
return MyCustomType(lhs.intValue * rhs.intValue)
}
func +=(inout lhs: MyCustomType, rhs: MyCustomType) {
lhs.myInt = (lhs.myInt ?? 0) + (rhs.myInt ?? 0)
}
Protocol MyFunctionalUtils (holding blueprints our additional generic array functions utilities) and thereafter, the extension of Array by MyFunctionalUtils; implementation of blue-printed method(s):
/* Protocol holding our function utilities, to be used as extension
o Array: blueprints for utility methods where Generator.Element
is constrained to MyTypes */
protocol MyFunctionalUtils {
func foo<T: MyTypes>(a: [T]) -> Int?
// ...
}
/* Extend array by protocol MyFunctionalUtils and implement blue-prints
therein for conformance */
extension Array : MyFunctionalUtils {
func foo<T: MyTypes>(a: [T]) -> Int? {
/* [T] is Self? proceed, otherwise return nil */
if let b = self.first {
if b is T && self.count == a.count {
var myMultSum: T = T(0)
for (i, sElem) in self.enumerate() {
myMultSum += (sElem as! T) * a[i]
}
return myMultSum.intValue
}
}
return nil
}
}
Finally, tests and two examples showing a function taking generic arrays, with the following cases, respectively
Showing implicit assertion that the array parameters conform to protocol 'MyFunctionalUtils', via type constraining the arrays elements to 'MyTypes' (function bar1).
Showing explicitly that the array parameters conform to protocol 'MyFunctionalUtils' (function bar2).
The test and examples follows:
/* Tests & examples */
let arr1d : [Double] = [1.0, 2.0, 3.0]
let arr2d : [Double] = [-3.0, -2.0, 1.0]
let arr1my : [MyCustomType] = [MyCustomType(1), MyCustomType(2), MyCustomType(3)]
let arr2my : [MyCustomType] = [MyCustomType(-3), MyCustomType(-2), MyCustomType(1)]
/* constrain array elements to MyTypes, hence _implicitly_ constraining
array parameters to protocol MyFunctionalUtils. However, this
conformance is not apparent just by looking at the function signature... */
func bar1<U: MyTypes> (arr1: [U], _ arr2: [U]) -> Int? {
return arr1.foo(arr2)
}
let myInt1d = bar1(arr1d, arr2d) // -4, OK
let myInt1my = bar1(arr1my, arr2my) // -4, OK
/* constrain the array itself to protocol MyFunctionalUtils; here, we
see directly in the function signature that conformance to
MyFunctionalUtils is given for valid array parameters */
func bar2<T: MyTypes, U: protocol<MyFunctionalUtils, _ArrayType> where U.Generator.Element == T> (arr1: U, _ arr2: U) -> Int? {
// OK, type U behaves as array type with elements T (=MyTypes)
var a = arr1
var b = arr2
a.append(T(2)) // add 2*7 to multsum
b.append(T(7))
return a.foo(Array(b))
/* Ok! */
}
let myInt2d = bar2(arr1d, arr2d) // 10, OK
let myInt2my = bar2(arr1my, arr2my) // 10, OK
import Foundation
extension Array {
func calculateMean() -> Double {
// is this an array of Doubles?
if self.first is Double {
// cast from "generic" array to typed array of Doubles
let doubleArray = self.map { $0 as! Double }
// use Swift "reduce" function to add all values together
let total = doubleArray.reduce(0.0, combine: {$0 + $1})
let meanAvg = total / Double(self.count)
return meanAvg
} else {
return Double.NaN
}
}
func calculateMedian() -> Double {
// is this an array of Doubles?
if self.first is Double {
// cast from "generic" array to typed array of Doubles
var doubleArray = self.map { $0 as! Double }
// sort the array
doubleArray.sort( {$0 < $1} )
var medianAvg : Double
if doubleArray.count % 2 == 0 {
// if even number of elements - then mean average the middle two elements
var halfway = doubleArray.count / 2
medianAvg = (doubleArray[halfway] + doubleArray[halfway - 1]) / 2
} else {
// odd number of elements - then just use the middle element
medianAvg = doubleArray[doubleArray.count / 2 ]
}
return medianAvg
} else {
return Double.NaN
}
}
}
Extention Array Find Index:
extension Array where Element: Equatable {
func findElementArrayIndex(findElement: String) -> Int {
var indexValue: Int = 0
var search = self.filter { findElement.isEmpty || "\($0)".contains(findElement)}
//print("search: \(search)")
for i in 0..<self.count {
if self[i] == search[0] {
indexValue = i
break
}
}
return indexValue
}
}
How can I extend Swift's Array<T> or T[] type with custom functional utils?
Browsing around Swift's API docs shows that Array methods are an extension of the T[], e.g:
extension T[] : ArrayType {
//...
init()
var count: Int { get }
var capacity: Int { get }
var isEmpty: Bool { get }
func copy() -> T[]
}
When copying and pasting the same source and trying any variations like:
extension T[] : ArrayType {
func foo(){}
}
extension T[] {
func foo(){}
}
It fails to build with the error:
Nominal type T[] can't be extended
Using the full type definition fails with Use of undefined type 'T', i.e:
extension Array<T> {
func foo(){}
}
And it also fails with Array<T : Any> and Array<String>.
Curiously Swift lets me extend an untyped array with:
extension Array {
func each(fn: (Any) -> ()) {
for i in self {
fn(i)
}
}
}
Which it lets me call with:
[1,2,3].each(println)
But I can't create a proper generic type extension as the type seems to be lost when it flows through the method, e.g trying to replace Swift's built-in filter with:
extension Array {
func find<T>(fn: (T) -> Bool) -> T[] {
var to = T[]()
for x in self {
let t = x as T
if fn(t) {
to += t
}
}
return to
}
}
But the compiler treats it as untyped where it still allows calling the extension with:
["A","B","C"].find { $0 > "A" }
And when stepped-thru with a debugger indicates the type is Swift.String but it's a build error to try access it like a String without casting it to String first, i.e:
["A","B","C"].find { ($0 as String).compare("A") > 0 }
Does anyone know what's the proper way to create a typed extension method that acts like the built-in extensions?
For extending typed arrays with classes, the below works for me (Swift 2.2). For example, sorting a typed array:
class HighScoreEntry {
let score:Int
}
extension Array where Element == HighScoreEntry {
func sort() -> [HighScoreEntry] {
return sort { $0.score < $1.score }
}
}
Trying to do this with a struct or typealias will give an error:
Type 'Element' constrained to a non-protocol type 'HighScoreEntry'
Update:
To extend typed arrays with non-classes use the following approach:
typealias HighScoreEntry = (Int)
extension SequenceType where Generator.Element == HighScoreEntry {
func sort() -> [HighScoreEntry] {
return sort { $0 < $1 }
}
}
In Swift 3 some types have been renamed:
extension Sequence where Iterator.Element == HighScoreEntry
{
// ...
}
After a while trying different things the solution seems to remove the <T> from the signature like:
extension Array {
func find(fn: (T) -> Bool) -> [T] {
var to = [T]()
for x in self {
let t = x as T;
if fn(t) {
to += t
}
}
return to
}
}
Which now works as intended without build errors:
["A","B","C"].find { $0.compare("A") > 0 }
Extend all types:
extension Array where Element: Any {
// ...
}
Extend Comparable types:
extension Array where Element: Comparable {
// ...
}
Extend some types:
extension Array where Element: Comparable & Hashable {
// ...
}
Extend a particular type:
extension Array where Element == Int {
// ...
}
I had a similar problem - wanted to extend the general Array with a swap() method, which was supposed to take an argument of the same type as the array. But how do you specify the generic type? I found by trial and error that the below worked:
extension Array {
mutating func swap(x:[Element]) {
self.removeAll()
self.appendContentsOf(x)
}
}
The key to it was the word 'Element'. Note that I didn't define this type anywhere, it seems automatically exist within the context of the array extension, and refer to whatever the type of the array's elements is.
I am not 100% sure what's going on there, but I think it is probably because 'Element' is an associated type of the Array (see 'Associated Types' here https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Generics.html#//apple_ref/doc/uid/TP40014097-CH26-ID189)
However, I can't see any reference of this in the Array structure reference (https://developer.apple.com/library/prerelease/ios/documentation/Swift/Reference/Swift_Array_Structure/index.html#//apple_ref/swift/struct/s:Sa)... so I'm still a little unsure.
Using Swift 2.2:
I ran into a similar issue when trying to remove duplicates from an array of strings. I was able to add an extension on the Array class that does just what I was looking to do.
extension Array where Element: Hashable {
/**
* Remove duplicate elements from an array
*
* - returns: A new array without duplicates
*/
func removeDuplicates() -> [Element] {
var result: [Element] = []
for value in self {
if !result.contains(value) {
result.append(value)
}
}
return result
}
/**
* Remove duplicate elements from an array
*/
mutating func removeDuplicatesInPlace() {
var result: [Element] = []
for value in self {
if !result.contains(value) {
result.append(value)
}
}
self = result
}
}
Adding these two methods to the Array class allows me to call one of the two methods on an array and successfully remove duplicates. Note that the elements in the array must conform to the Hashable protocol. Now I can do this:
var dupes = ["one", "two", "two", "three"]
let deDuped = dupes.removeDuplicates()
dupes.removeDuplicatesInPlace()
// result: ["one", "two", "three"]
If you want to learn about extending Arrays and other types of build in classes checkout code in this github repo https://github.com/ankurp/Cent
As of Xcode 6.1 the syntax to extend arrays is as follows
extension Array {
func at(indexes: Int...) -> [Element] {
... // You code goes herer
}
}
I had a look at the Swift 2 standard library headers, and here is the prototype for the filter function, which makes it quite obvious how to roll your own.
extension CollectionType {
func filter(#noescape includeElement: (Self.Generator.Element) -> Bool) -> [Self.Generator.Element]
}
It's not an extension to Array, but to CollectionType, so the same method applies to other collection types. #noescape means that the block passed in will not leave the scope of the filter function, which enables some optimisations. Self with a capital S is the class we are extending. Self.Generator is an iterator that iterates through the objects in the collection and Self.Generator.Element is the type of the objects, for example for an array [Int?] Self.Generator.Element would be Int?.
All in all this filter method can be applied to any CollectionType, it needs a filter block which takes an element of the collection and returns a Bool, and it returns an array of the original type. So putting this together, here's a method that I find useful: It combines map and filter, by taking a block that maps a collection element to an optional value, and returns an array of those optional values that are not nil.
extension CollectionType {
func mapfilter<T>(#noescape transform: (Self.Generator.Element) -> T?) -> [T] {
var result: [T] = []
for x in self {
if let t = transform (x) {
result.append (t)
}
}
return result
}
}
import Foundation
extension Array {
var randomItem: Element? {
let idx = Int(arc4random_uniform(UInt32(self.count)))
return self.isEmpty ? nil : self[idx]
}
}
(Swift 2.x)
You can also extend the array to conform to a protocol containing blue-rpints for generic type methods, e.g., a protocol containing your custom functional utils for all generic array elements conforming to some type constraint, say protocol MyTypes. The bonus using this approach is that you can write functions taking generic array arguments, with a constraint that these array arguments must conform to your custom function utilities protocol, say protocol MyFunctionalUtils.
You can get this behaviour either implicitly, by type constraining the array elements to MyTypes, or---as I will show in the method I describe below---, quite neatly, explicitly, letting your generic array functions header directly show that input arrays conforms to MyFunctionalUtils.
We begin with Protocols MyTypes for use as type constraint; extend the types you want to fit in your generics by this protocol (example below extends fundamental types Int and Double as well as a custom type MyCustomType)
/* Used as type constraint for Generator.Element */
protocol MyTypes {
var intValue: Int { get }
init(_ value: Int)
func *(lhs: Self, rhs: Self) -> Self
func +=(inout lhs: Self, rhs: Self)
}
extension Int : MyTypes { var intValue: Int { return self } }
extension Double : MyTypes { var intValue: Int { return Int(self) } }
// ...
/* Custom type conforming to MyTypes type constraint */
struct MyCustomType : MyTypes {
var myInt : Int? = 0
var intValue: Int {
return myInt ?? 0
}
init(_ value: Int) {
myInt = value
}
}
func *(lhs: MyCustomType, rhs: MyCustomType) -> MyCustomType {
return MyCustomType(lhs.intValue * rhs.intValue)
}
func +=(inout lhs: MyCustomType, rhs: MyCustomType) {
lhs.myInt = (lhs.myInt ?? 0) + (rhs.myInt ?? 0)
}
Protocol MyFunctionalUtils (holding blueprints our additional generic array functions utilities) and thereafter, the extension of Array by MyFunctionalUtils; implementation of blue-printed method(s):
/* Protocol holding our function utilities, to be used as extension
o Array: blueprints for utility methods where Generator.Element
is constrained to MyTypes */
protocol MyFunctionalUtils {
func foo<T: MyTypes>(a: [T]) -> Int?
// ...
}
/* Extend array by protocol MyFunctionalUtils and implement blue-prints
therein for conformance */
extension Array : MyFunctionalUtils {
func foo<T: MyTypes>(a: [T]) -> Int? {
/* [T] is Self? proceed, otherwise return nil */
if let b = self.first {
if b is T && self.count == a.count {
var myMultSum: T = T(0)
for (i, sElem) in self.enumerate() {
myMultSum += (sElem as! T) * a[i]
}
return myMultSum.intValue
}
}
return nil
}
}
Finally, tests and two examples showing a function taking generic arrays, with the following cases, respectively
Showing implicit assertion that the array parameters conform to protocol 'MyFunctionalUtils', via type constraining the arrays elements to 'MyTypes' (function bar1).
Showing explicitly that the array parameters conform to protocol 'MyFunctionalUtils' (function bar2).
The test and examples follows:
/* Tests & examples */
let arr1d : [Double] = [1.0, 2.0, 3.0]
let arr2d : [Double] = [-3.0, -2.0, 1.0]
let arr1my : [MyCustomType] = [MyCustomType(1), MyCustomType(2), MyCustomType(3)]
let arr2my : [MyCustomType] = [MyCustomType(-3), MyCustomType(-2), MyCustomType(1)]
/* constrain array elements to MyTypes, hence _implicitly_ constraining
array parameters to protocol MyFunctionalUtils. However, this
conformance is not apparent just by looking at the function signature... */
func bar1<U: MyTypes> (arr1: [U], _ arr2: [U]) -> Int? {
return arr1.foo(arr2)
}
let myInt1d = bar1(arr1d, arr2d) // -4, OK
let myInt1my = bar1(arr1my, arr2my) // -4, OK
/* constrain the array itself to protocol MyFunctionalUtils; here, we
see directly in the function signature that conformance to
MyFunctionalUtils is given for valid array parameters */
func bar2<T: MyTypes, U: protocol<MyFunctionalUtils, _ArrayType> where U.Generator.Element == T> (arr1: U, _ arr2: U) -> Int? {
// OK, type U behaves as array type with elements T (=MyTypes)
var a = arr1
var b = arr2
a.append(T(2)) // add 2*7 to multsum
b.append(T(7))
return a.foo(Array(b))
/* Ok! */
}
let myInt2d = bar2(arr1d, arr2d) // 10, OK
let myInt2my = bar2(arr1my, arr2my) // 10, OK
import Foundation
extension Array {
func calculateMean() -> Double {
// is this an array of Doubles?
if self.first is Double {
// cast from "generic" array to typed array of Doubles
let doubleArray = self.map { $0 as! Double }
// use Swift "reduce" function to add all values together
let total = doubleArray.reduce(0.0, combine: {$0 + $1})
let meanAvg = total / Double(self.count)
return meanAvg
} else {
return Double.NaN
}
}
func calculateMedian() -> Double {
// is this an array of Doubles?
if self.first is Double {
// cast from "generic" array to typed array of Doubles
var doubleArray = self.map { $0 as! Double }
// sort the array
doubleArray.sort( {$0 < $1} )
var medianAvg : Double
if doubleArray.count % 2 == 0 {
// if even number of elements - then mean average the middle two elements
var halfway = doubleArray.count / 2
medianAvg = (doubleArray[halfway] + doubleArray[halfway - 1]) / 2
} else {
// odd number of elements - then just use the middle element
medianAvg = doubleArray[doubleArray.count / 2 ]
}
return medianAvg
} else {
return Double.NaN
}
}
}
Extention Array Find Index:
extension Array where Element: Equatable {
func findElementArrayIndex(findElement: String) -> Int {
var indexValue: Int = 0
var search = self.filter { findElement.isEmpty || "\($0)".contains(findElement)}
//print("search: \(search)")
for i in 0..<self.count {
if self[i] == search[0] {
indexValue = i
break
}
}
return indexValue
}
}