Is it possible to filter an array of [AnyObject] to yield all elements of a given type, and none other?
I can do it if the type is known at compile time:
class MyClass1: CustomStringConvertible {
var value: Int
var description: String {
return "MyClass1: \(value)"
}
init(_ value: Int) {
self.value = value
}
}
class MyClass2: CustomStringConvertible {
var value: Int
var description: String {
return "MyClass1: \(value)"
}
init(_ value: Int) {
self.value = value
}
}
class MySubClass1: MyClass1 {
override var description: String {
return "MySubClass1: \(value)"
}
}
let a1 = MySubClass1(1)
let a2 = MySubClass1(2)
let b1 = MyClass1(3)
let b2 = MyClass2(4)
let array: [AnyObject] = [a1, b1, a2, b2]
func getClass1ObjectsFromArray(_ array: [AnyObject]) -> [MyClass1] {
return array.compactMap( { $0 as? MyClass1 })
}
func getSubClass1ObjectsFromArray(_ array: [AnyObject]) -> [MySubClass1] {
return array.compactMap( { $0 as? MySubClass1 })
}
print(getClass1ObjectsFromArray(array))
print(getSubClass1ObjectsFromArray(array))
Prints:
[MySubClass1: 1, MyClass1: 3, MySubClass1: 2]
[MySubClass1: 1, MySubClass1: 2]
For every type I want to filter on, I had to write a separate function. This looks ugly to me, and will not work when the type to be selected for is only known at run time.
Question:
Is there a generic way to write such a function? Preferably something like:
func getObjectsOfType(_ type: TypeExpression, fromArray array: [AnyObject])
-> [TypeExpression] {
...
}
Or any other way to achieve this?
Thanks for any help!
I think you could use something like this...
let filteredArray = array.compactMap { $0 as? RequiredType }
This will filter the array and return a typed array containing only the type you want.
Caveat
Having said that. In Swift you should be avoiding heterogeneous arrays where possible. Arrays should really only contain one type of item.
A bit of code testing...
Tested in Playground...
let array: [Any] = [1, "hello", 3, 3.1415, "world"]
let filteredArray = array.compactMap { $0 as? String }
filteredArray
Output:
filteredArray = ["hello", "world"]
👍🏻
Edit 1
You could also create a generic function something like this...
func filter<T>(array: [Any]) -> [T] {
return array.compactMap { $0 as? T }
}
let filteredArray: [String] = filter(array: array)
This will then filter based on the type of the output array that you want.
I'm not sure what you mean by only knowing the type you want at run time. Can you give a more concrete example of what you mean?
Edit 2
Another possibility is a generic function like this...
func filter<T>(array: [Any], byType typeObject: T) -> [T] {
return array.compactMap { $0 as? T }
}
let filteredArray = filter(array: array, byType: "some string")
This uses the type information of the second parameter to filter the array by that type of item.
Edit 3
If you don't like passing in an instance of the type then you can pass the type itself...
func filter<T>(array: [Any], byType typeObject: T.Type) -> [T] {
return array.compactMap { $0 as? T }
}
let filteredArray = filter(array: array, byType: String.self)
But I'm not sure what more you're getting from this than just filtering by string in the first place?
Related
Given this code...
class Vehicle{}
class Car : Vehicle {}
class Honda : Car {}
How would you write the function 'findFirst' below...
class TypeManager {
var managedTypes:[Any.Type]?
func findFirst(_ type:Any.Type) -> Any.Type? {
return managedTypes.first{ t in t is type.Type } // <-- Doesn't like 'type'
}
}
var typeManager = TypeManager()
typeManager.managedTypes = [
String.self,
Int.self,
Honda.self
]
let firstCarType = typeManager.findFirst(Car.Type)
Note: This is actually doing a reverse-key-lookup on a dictionary. In a perfect solution, I'd first try finding an exact match on 'type', and if not found, settle for a subclass of 'type'. I just simplified the (faked) code to focus on the matching portion.
To expand upon Martin R's great answer you can make an array extension like the following:
extension Array {
func first<T>(ofType: T.Type) -> T.Type? {
return first { $0 is T.Type } as? T.Type
}
func first<T>(ofExactType type: T.Type) -> T.Type? {
return first { $0 as? Any.Type == type } as? T.Type
}
}
class Vehicle {}
class Car : Vehicle {}
class Honda: Car {}
let carTypes = [Honda.self, Vehicle.self, Car.self] // Inferred type [Vehicle]
print(carTypes.first(ofType: Car.self) ?? "n/a") // prints Honda
print(carTypes.first(ofExactType: Car.self) ?? "n/a") // prints Car
Also, just FYI, $0 as? Any.Type == type is the same as doing $0 as? Any.Type == T.self. Either one would work.
Classes are instances of a meta-type and can be checked with is and as?.
You can use a generic function to pass in the sought type:
class TypeManager {
var managedTypes:[Any.Type] = []
func findFirst<T>(_: T.Type) -> Any.Type? {
return managedTypes.first { $0 is T.Type }
}
}
Example:
if let firstCarType = typeManager.findFirst(Car.self) {
print(firstCarType) // Honda
}
Or with conditional binding and compactMap:
class TypeManager {
var managedTypes:[Any.Type] = []
func findFirst<T>(_: T.Type) -> T.Type? {
return managedTypes.compactMap { $0 as? T.Type }.first
}
}
This has the advantage that the returned type is T.Type? and not Any.Type?. (Use managedTypes.lazy.compactMap if the list can be large and short circuiting is wanted.)
For simplification. Lets say i have some unique values -> the numbers from 1 to 10
Now I want 1-5 map to the value "first" and I want 6-10 map to the value "second"
Is there a way I can create or extend a dictionary to work like the following?
let dict: [Range<Int> : String]
The goal is to have the following results:
print(dict[1]) // prints first
print(dict[2]) // prints first
print(dict[3]) // prints first
print(dict[7]) // prints second
print(dict[8]) // prints second
print(dict[9]) // prints second
The way I am currently doing it is to simply have the multiple keys map to the same value. But my dictionary can have sometimes 60k values. So I am wondering if a range can work.
I know I can make the value into a class instead of a struct so that multiple keys can map to the same class object, but I was wondering if simply creating a Dictionary that worked like above was possible?
If you insist on using Dictionary, you have to wait until Swift 3.1 (currently in beta):
extension CountableClosedRange : Hashable {
public var hashValue: Int {
return "\(lowerBound) to \(upperBound)".hashValue
}
}
// This feature is called concrete-type extension and requires Swift 3.1
extension Dictionary where Key == CountableClosedRange<Int> {
subscript(rawValue rawValue: Int) -> Value? {
for k in self.keys {
if k ~= rawValue {
return self[k]
}
}
return nil
}
}
let dict : [CountableClosedRange<Int>: String] = [
1...5: "first",
6...10: "second"
]
print(dict[rawValue: 1])
print(dict[rawValue: 2])
print(dict[rawValue: 3])
print(dict[rawValue: 7])
print(dict[rawValue: 8])
print(dict[rawValue: 9])
However, it's a lot clearer if you implement your own data model:
struct MyRange {
var ranges = [CountableClosedRange<Int>]()
var descriptions = [String]()
mutating func append(range: CountableClosedRange<Int>, description: String) {
// You can check for overlapping range here if you want
self.ranges.append(range)
self.descriptions.append(description)
}
subscript(value: Int) -> String? {
for (i, range) in self.ranges.enumerated() {
if range ~= value {
return descriptions[i]
}
}
return nil
}
}
var range = MyRange()
range.append(range: 1...5, description: "one")
range.append(range: 6...10, description: "second")
print(range[1])
print(range[2])
print(range[6])
print(range[7])
print(range[100])
This is in Swift 3.0, it may not be as nice as Code Different's answer though.
class MyRange: Hashable, Equatable {
public var hashValue: Int {
get {
return (self.range.lowerBound + self.range.upperBound).hashValue
}
}
var range: Range<Int>!
public static func ==(_ lhs: MyRange, _ rhs: MyRange) -> Bool {
return lhs.range == rhs.range
}
init(range: Range<Int>) {
self.range = range
}
}
extension Dictionary where Key: MyRange, Value: ExpressibleByStringLiteral {
internal subscript(index: Int) -> [String] {
return self.filter({$0.key.range.contains(index)}).map({$0.value as! String})
}
}
Now, you can make your dictionary like so:
var dict = Dictionary<MyRange, String>()
dict[MyRange(range: 0..<5)] = "first"
dict[MyRange(range: 5..<10)] = "second"
Getting values works with Integers and Ranges:
print(dict[1]) // ["first"]
print(dict[5]) // ["second"]
print(dict[11]) // []
print(dict[MyRange(range: 0..<5)]) // "first"
print(dict[MyRange(range: 0..<6)]) // nil
The dictionary should look like this:
print(dict)
// [MyRange: "first", MyRange: "second"]
Adding an extension to Array, which returns the first Int or String is easy:
extension Array {
func firstInt() -> Int? {
return self.flatMap{$0 as? Int}.first
}
func firstString() -> String? {
return self.flatMap{$0 as? String}.first
}
}
let a1:[AnyObject?] = [nil, "abc", 3, 4]
let a2:[AnyObject?] = [nil, [3], [ "foo":"bar" ]]
print(a1.firstInt()) // Optional(3)
print(a2.firstInt()) // nil
print(a1.firstString()) // Optional("abc")
print(a2.firstString()) // nil
I can define a generic version, but I am not able to figure out how to call it because it does not take any parameter. Without a parameter, I can't specify the type!
extension Array {
func firstValueOfType<T>() -> T? {
return self.flatMap{$0 as? T}.first
}
}
// I can't figure out how to call this method!
I can work around it by adding a dummy parameter, but this is ugly.
extension Array {
func firstValueLike<T>(_:T) -> T? {
return self.flatMap{$0 as? T}.first
}
}
let a1:[AnyObject?] = [nil, "abc", 3, 4]
print(a1.firstValueLike(1)) // Optional(3)
print(a1.firstValueLike("")) // Optional("abc")
I'd appreciate if somebody could tell me how to call firstValueOfType function (or alternative way to define a generic function cleanly).
Additional Info
"Cannot explicitly specialize a generic function" is similar, but my problem is a bit more complicated because of Optional.
I've got a great answer from OOPer, which even includes the better implementation which uses lazy.filter, instead of flatMap.
extension Array {
func firstValueOfType<T>() -> T? {
return self.lazy.filter {$0 is T}.first as? T
}
}
let a1:[AnyObject?] = [nil, "abc", 3, 4]
print(a1.firstValueOfType() as Int?) // Optional(3)
print(a1.firstValueOfType() as String?) // Optional("abc")
Thank you very much for a very quick support!
One way is assigning the result to a variable with explicit type.
let i: Int? = a1.firstValueOfType()
print(i) // Optional(3)
let s: String? = a1.firstValueOfType()
print(s) // Optional("abc")
Another is using as:
print(a1.firstValueOfType() as Int?) // Optional(3)
print(a1.firstValueOfType() as String?) // Optional("abc")
You can pass the type as an argument with T.Type, like so:
extension Array {
func firstValue<T>(like type: T.Type) -> T? {
return self.flatMap{$0 as? T}.first
}
}
[1,2,3].firstValue(like: Int.self)
Say I have a collection of objects inheriting from a common superclass (this is preferable to protocols in this case):
class ObjectSuperClass {
type: ObjectType
}
class ObjectClass1: ObjectSuperClass {
type = .Type1
}
class ObjectClass2: ObjectSuperClass {
type = .Type2
}
I'm looking to create a generic search function like this:
func objectsOfType<T: ObjectSuperClass>(T.class, otherFilter: Any?) -> [T]
Which could be used to search for a given sub-type, returning a more specific array of results:
let result = objectsOfType(ObjectClass2.class, otherFilter: nil) -> [ObjectClass2]
(pseudo-swift)
I feel like this is somewhere generics could help, but cannot see where constraints should be placed. Is it possible?
Well remarkably this works...
func filterType<T>(list: [AnyObject]) -> [T]
{
return list.filter{ $0 is T }.map{ $0 as! T }
}
...provided you assign the result to something that has been explicitly typed, as in the following example:
class ObjectSuperClass: CustomStringConvertible
{
let myType: String
init(aString: String)
{
myType = aString
}
var description: String { return myType }
}
class ObjectClass1: ObjectSuperClass
{
init()
{
super.init(aString: "<t 1>")
}
}
class ObjectClass2: ObjectSuperClass
{
init()
{
super.init(aString: "<t 2>")
}
}
let unfilteredList: [AnyObject] = [ ObjectClass1(), ObjectClass2(), ObjectSuperClass(aString: "<Who knows>")]
let filteredList1: [ObjectClass1] = filterType(list: unfilteredList)
print("\(filteredList1)") // <t 1>
let filteredList2: [ObjectClass2] = filterType(list: unfilteredList)
print("\(filteredList2)") // <t 2>
let filteredList3: [ObjectSuperClass] = filterType(list: unfilteredList)
print("\(filteredList3)") // [<t 1>, <t 2>, <Who knows>]
T is inferred in each case from the requested return type. The function itself filters the original array based on whether the elements are of the required type and then force casts the filtered results to the correct type.
If you want an "extra filter" you don't need to explicitly type the results as long as T can be inferred from your extra filter function.
func extraFilterType<T>(list: [AnyObject], extraFilter: T -> Bool) -> [T]
{
return list.filter{ $0 is T }.map{ $0 as! T }.filter(extraFilter)
}
let filteredList = extraFilterType(unfilteredList){
(element : ObjectClass2) -> Bool in
!element.description.isEmpty
}
print("\(filteredList)") // <t 2>
EDIT
A slicker version of the filterType function would use flatMap()
func filterType<T>(list: [Any]) -> [T]
{
return list.flatMap{ $0 as? T }
}
EDIT 2
Flatmap is deprecated for optionals, since Swift 4.something, use compactMap
func filterType<T>(list: [Any]) -> [T]
{
return list.compactMap{ $0 as? T }
}
This is the closest approximation I can come up with:
func objectsOfType<T: ObjectSuperClass>(type type: T.Type) -> [T] {
// Just returns an array of all objects of given type
}
func objectsOfType<T: ObjectSuperClass>(type type: T.Type, predicate: T -> Bool) -> [T] {
// Uses predicate to filter out objects of given type
}
Usage:
let bar = objectsOfType(type: ObjectClass1.self)
let baz = objectsOfType(type: ObjectClass2.self) {
// Something that returns Bool and uses $0
}
Technically, you can also go without type argument in the above, but then you will need to have explicitly typed receivers (bar and baz in the above example) so that Swift can correctly infer the types for you and use the right version of the generic function.
You can implement the function like this:
func objectsOfType<T: ObjectSuperClass>(objects: [ObjectSuperClass], subclass: T.Type, otherFilter: (T->Bool)?) -> [T] {
if let otherFilter = otherFilter {
return objects.filter{$0 is T && otherFilter($0 as! T)}.map{$0 as! T}
} else {
return objects.filter{$0 is T}.map{$0 as! T}
}
}
Usage example:
objectsOfType(arrayOfObjects, subclass: ObjectClass1.self, otherFilter: nil)
Note that I'm not a fan of forced casting, however in this scenario it should not cause problems.
Or, the more verbose version of the function, with one less forced cast:
func objectsOfType<T: ObjectSuperClass>(objects: [ObjectSuperClass], subclass: T.Type, otherFilter: (T->Bool)?) -> [T] {
return objects.filter({object in
if let object = object as? T {
if let otherFilter = otherFilter {
return otherFilter(object)
} else {
return true
}
} else {
return false
}
}).map({object in
return object as! T
})
}
I have a Set of instances of type Thingie, and I want to provide arrays of Thingies sorted on any property of Thingie. Some of the properties are Int, for instance, while others are String, and there could be others. So I wanted to create a sort routine that accepts a string as the name of the property and compares the two properties of two thingies to determine the order.
It seemed like a job for generics, and I'm getting close, but there's a hole.
Here's where I'm at right now:
func compare<T:Comparable>(lft: T, _ rgt: T) -> Bool {
return lft < rgt
}
func orderBy(sortField: String) -> [Thingie] {
let allArray = (self.thingies as NSSet).allObjects as! [Thingie]
//typealias T = the type of allArray[0][sortField]
// or maybe create an alias that conforms to a protocol:
//typealias T:Comparable = ?
return allArray.sort({(a, b) -> Bool in
return self.compare(a[sortField] as! T, b[sortField] as! T)
})
}
I created a compare function using generics, and invoke it in my sort routine. The catch is that AnyObject! will not work for my generic, so I need to cast the values returned from a[sortField] and b[sortField] to be of the same type. It doesn't even really matter what type as long as the compiler is happy that both values are of the same type and that it implements the Comparable protocol.
I figured a typealias would do the trick, but maybe there's a better way?
Side question: surely there's a better way to create the initial, unsorted array from the set without resorting to NSSet. A little hint would be welcome. [Solved that bit! Thanks, Oliver Atkinson!]
Here's a big 'ol chunk of code you can paste into a playground. It has three attempts at the orderBy implementation, each with a problem.
//: Playground - noun: a place where people can play
import Foundation
class Thingie: Hashable {
var data: [String: AnyObject]
var hashValue: Int
init(data: [String: AnyObject]) {
self.data = data
self.hashValue = (data["id"])!.hashValue
}
subscript(propName: String) -> AnyObject! {
return self.data[propName]
}
}
func ==(lhs: Thingie, rhs: Thingie) -> Bool {
return lhs.hashValue == rhs.hashValue
}
var thingies: Set = Set<Thingie>()
thingies.insert(Thingie(data: ["id": 2, "description": "two"]));
thingies.insert(Thingie(data: ["id": 11, "description": "eleven"]));
// attempt 1
// won't compile because '<' won't work when type is ambiguous e.g., AnyObject
func orderByField1(sortField: String) -> [Thingie] {
return thingies.sort { $0[sortField] < $1[sortField] }
}
// compare function that promises the compiler that the operands for < will be of the same type:
func compare<T:Comparable>(lft: T, _ rgt: T) -> Bool {
return lft < rgt
}
// attempt 2
// This compiles but will bomb at runtime if Thingie[sortField] is not a string
func orderByField2(sortField: String) -> [Thingie] {
return thingies.sort { compare($0[sortField] as! String, $1[sortField] as! String) }
}
// attempt 3
// Something like this would be ideal, but protocol Comparable can't be used like this.
// I suspect the underlying reason that Comparable can't be used as a type is the same thing preventing me from making this work.
func orderByField3(sortField: String) -> [Thingie] {
return thingies.sort { compare($0[sortField] as! Comparable, $1[sortField] as! Comparable) }
}
// tests - can't run until a compiling candidate is written, of course
// should return array with thingie id=2 first:
var thingieList: Array = orderByField2("id");
print(thingieList[0]["id"])
// should return array with thingie id=11 first:
var thingieList2: Array = orderByField2("description");
print(thingieList2[0]["id"])
My previous answer, though it works, does not make the most of the Swift's excellent type checker. It also switches between the types that can be used in one centralised place which limits extensibility to the framework owner.
The following approach solves these issues. (Please forgive me for not having the heart to delete my previous answer; let us say that it's limitations are instructive...)
As before, we'll start with the target API:
struct Thing : ThingType {
let properties: [String:Sortable]
subscript(key: String) -> Sortable? {
return properties[key]
}
}
let data: [[String:Sortable]] = [
["id": 1, "description": "one"],
["id": 2, "description": "two"],
["id": 3, "description": "three"],
["id": 4, "description": "four"],
["id": 4, "description": "four"]
]
var things = data.map(Thing.init)
things.sortInPlaceBy("id")
things
.map{ $0["id"]! } // [1, 2, 3, 4]
things.sortInPlaceBy("description")
things
.map{ $0["description"]! } // ["four", "one", "three", "two"]
To make this possible we must have this ThingType protocol and an extension to mutable collections (which will work for sets as well as arrays):
protocol ThingType {
subscript(_: String) -> Sortable? { get }
}
extension MutableCollectionType
where Index : RandomAccessIndexType, Generator.Element : ThingType
{
mutating func sortInPlaceBy(key: String, ascending: Bool = true) {
sortInPlace {
guard let lhs = $0[key], let rhs = $1[key] else {
return false // TODO: nil handling
}
guard let b = (try? lhs.isOrderedBefore(rhs, ascending: ascending)) else {
return false // TODO: handle SortableError
}
return b
}
}
}
Evidently, the whole idea revolves around this Sortable protocol:
protocol Sortable {
func isOrderedBefore(_: Sortable, ascending: Bool) throws -> Bool
}
... which can be conformed to independently by any type we want to work with:
import Foundation
extension NSNumber : Sortable {
func isOrderedBefore(other: Sortable, ascending: Bool) throws -> Bool {
try throwIfTypeNotEqualTo(other)
let f: (Double, Double) -> Bool = ascending ? (<) : (>)
return f(doubleValue, (other as! NSNumber).doubleValue)
}
}
extension NSString : Sortable {
func isOrderedBefore(other: Sortable, ascending: Bool) throws -> Bool {
try throwIfTypeNotEqualTo(other)
let f: (String, String) -> Bool = ascending ? (<) : (>)
return f(self as String, other as! String)
}
}
// TODO: make more types Sortable (including those that do not conform to NSObject or even AnyObject)!
This throwIfTypeNotEqualTo method is just a convenience extension of Sortable:
enum SortableError : ErrorType {
case TypesNotEqual
}
extension Sortable {
func throwIfTypeNotEqualTo(other: Sortable) throws {
guard other.dynamicType == self.dynamicType else {
throw SortableError.TypesNotEqual
}
}
}
And that's it. Now we can conform new types to Sortable even outside of the framework and the type checker is validating our [[String:Sortable]] source data at compile time. Also, if Thing is extended to conform to Hashable then Set<Thing> will also be sortable by key...
Note that, although Sortable is itself unconstrained (which is awesome), source data and Thing's properties can be constrained to dictionaries with NSObject or AnyObject values if required by making use of a protocol like:
protocol SortableNSObjectType : Sortable, NSObjectProtocol { }
... or more directly by declaring data and Thing's properties as:
let _: [String : protocol<Sortable, NSObjectProtocol>]
I don't know the implementation of Thingie but maybe you could provide more context.
You could however go for something like this
func orderBy(sortField: String) -> [Thingie] {
return thingies.allObjects.map { $0 as! Thingie }.sort { $0[sortField] < $1[sortField] }
}
If you could provide a playground example so I can provide further help.
Also why did you use NSSet rather than a swift Set? would that give you what you want
let thingies: Set = Set<Thingie>()
func orderBy(sortField: String) -> [Thingie] {
return thingies.sort { $0[sortField] < $1[sortField] }
}
edit:
The trouble is with swift's type safety - it requires you to know what types you are dealing with so that it can compile correctly - if you specify the actual type when you want to order the field you can get it to work as expected.
func orderByField<T: Comparable>(sortField: String, type: T.Type) -> [Thingie] {
return thingies.sort { ($0[sortField] as? T) < ($1[sortField] as? T) }
}
var thingieList: Array = orderByField("id", type: Int.self);
print(thingieList[0]["id"])
var thingieList2: Array = orderByField("description", type: String.self);
print(thingieList2[0]["id"])
The above will print 2 then 11 - if you wanted to get around this you could store your objects in a different struct and then you can sort the array of 'Things' on the variable.
e.g.
struct Thing {
let id: Int
let description: String
}
var data: [Thing] = [
Thing(id: 2, description: "two"),
Thing(id: 11, description: "eleven")
]
let first = data.sort { $0.id < $1.id }.first?.id
let second = data.sort { $0.description < $1.description }.first?.id
print(first)
print(second)
Which would achieve the same thing - 2 and 11
I would advise against using AnyObject where possible as its trying to cheat the compiler into telling it you don't care for its help.
Its an interesting problem though and I hope this helps you towards your solution.
I will start with the target API (ignoring conformance to Hashable as its addition wont change anything in what follows). So, let's say we'd like to be able to write the following:
var thingies = [
["id": 1, "description": "one"],
["id": 2, "description": "two"],
["id": 3, "description": "three"],
["id": 4, "description": "four"]
].map(Thingie.init)
thingies.sortInPlace{ $0["id"] < $1["id"] }
... and even:
thingies.sortInPlaceBy("id")
thingies
.map{ $0["id"]!.value } // [1, 2, 3, 4]
thingies.sortInPlaceBy("description")
thingies
.map{ $0["description"]!.value } // ["four", "one", "three", "two"]
Obviously, we'd need an extension of MutableCollectionType protocol along the lines of:
protocol ThingieDatumSubscriptable {
subscript(_: String) -> ThingieDatum? { get }
}
extension Thingie : ThingieDatumSubscriptable {}
extension MutableCollectionType
where Index : RandomAccessIndexType, Generator.Element : ThingieDatumSubscriptable
{
mutating func sortInPlaceBy(datumName: String, ascending: Bool = true) {
let f: (ThingieDatum?, ThingieDatum?) -> Bool = ascending ? (<) : (>)
sortInPlace{ f($0[datumName], $1[datumName]) }
}
}
This ThingieDatum would then be something like:
import Foundation
struct ThingieDatum : Comparable {
let type: AnyObject.Type
let value: AnyObject
let name: String
init(keyValuePair: (String, AnyObject)) {
name = keyValuePair.0
value = keyValuePair.1
type = keyValuePair.1.dynamicType
}
}
... and its conformance to Comparable implemented in some sort of pedestrian way as follows (unless we introduce more protocols):
func == (lhs: ThingieDatum, rhs: ThingieDatum) -> Bool {
guard lhs.name == rhs.name && lhs.type == rhs.type else {
return false
}
switch lhs.type {
// TODO: implement for other types
case is NSNumber.Type: return lhs.value as! NSNumber == rhs.value as! NSNumber
case is NSString.Type: return (lhs.value as! String) == (rhs.value as! String)
default: break
}
return false
}
func < (lhs: ThingieDatum, rhs: ThingieDatum) -> Bool {
assert(lhs.name == rhs.name && lhs.type == rhs.type)
switch lhs.type {
// TODO: implement for other types
case is NSNumber.Type: return (lhs.value as! NSNumber).doubleValue < (rhs.value as! NSNumber).doubleValue
case is NSString.Type: return (lhs.value as! String) < (rhs.value as! String)
default: break
}
return false
}
Armed with such a ThingieDatum we can finally work out the Thingie itself:
struct Thingie {
var data: [ThingieDatum]
init(_ data: [String: AnyObject]) {
self.data = data.map(ThingieDatum.init)
}
subscript(datumName: String) -> ThingieDatum? {
for datum in data where datum.name == datumName {
return datum
}
return nil
}
}
And although this is, of course, all meant as a fun exercise, it does work (copy and paste into the playground if you can work our the correct order of snippets)... To take this idea further, however, we would probably want to constrain ThingiDatum initialiser to a custom protocol (rather than AnyObject), which would guarantee comparability. We would then conform to that protocol with each type we want to work with instead of switching through those types in one centralised place...