快速的对象数组符合协议

Question

I have a protocol like this:

protocol Datable {
    var date: NSDate { get set }
}

struct DEPref: Datable {
   var date: NSDate
}

struct DEPObs: Datable {
   var date: NSDate
}

func fetchDepRefs() -> [DEPRef] {...}
func fetchDepObss() -> [DEPObs] {...}

I would like to create an array of DEPref and DEPObs in order to sort the final list.

I have tried many things but the compiler complains. Example:

var depRefList: Array<Datable> = fetchDepRefs()
var depObsList: Array<Datable> = fetchDepObss()
var allDeps = ...

An error in the first line "Cannot convert value of type [DEPref] to specified type Array"

Answer 1

I'm very new to Swift/iOS programming, but something like this works for me.

func fetchDepRefs() -> Array<Datable> {return Array<Datable>()}

var depRefList = fetchDepRefs()
var testDEPref = DEPref(date: NSDate())
var testDEPref2 = DEPref(date: NSDate())

depRefList.append(testDEPref)
depRefList.append(testDEPref2)

for ref in depRefList {
    print(ref.date)
}

Your functions could also return [Datable]

eg.

func fetchDepRefs() -> [Datable] {return [Datable]()}

This also works for your scenario

Edit:

Or if you're looking for type safety in your functions, the following code will also work

func fetchDepRefs() -> [DEPref] {return [DEPref]()}
func fetchDepObss() -> [DEPObs] {return [DEPObs]()}

var depRefList = fetchDepRefs()
var depObsList = fetchDepObss()

var allDeps: [Datable] = [Datable]()

In this you can add elements from depRefList and depObsList to allDeps and everything will work fine.

Edit again:

This is a fully working example of what you're trying to achieve. In this I'm using the map function to transform the elements of the given arrays to Datable objects

protocol Datable {
    var date: NSDate { get set }
}

struct DEPref: Datable {
   var date: NSDate
}

struct DEPObs: Datable {
   var date: NSDate
}

func fetchDepRefs() -> [DEPref] {return [DEPref]()}
func fetchDepObs() -> [DEPObs] {return [DEPObs]()}

var depRefs = fetchDepRefs()
var depObs = fetchDepObs()

var ref1 = DEPref(date: NSDate())
var obs1 = DEPObs(date: NSDate())

depRefs.append(ref1)
depObs.append(obs1)

var allDeps = depRefs.map{$0 as Datable} + depObs.map{$0 as Datable}


for x in allDeps {
    print("I'm in allDeps array: \(x.date)")
}

Answer 2

Are you running Swift 2 on iOS? The following runs successfully on Swift 3.

http://swiftlang.ng.bluemix.net/#/repl/57b13a01133614f70db3347e

protocol Datable {
    var date: NSDate { get set }
}

struct Type1: Datable {
   var date: NSDate
}

struct Type2: Datable {
   var date: NSDate
}

var x : Datable = Type1(date:NSDate())
var y : Datable = Type2(date:NSDate())

var array : [Datable] = [x, y]

var x2 : Datable = Type1(date:NSDate())
var y2 : Datable = Type2(date:NSDate())

array.append(x2)
array.append(y2)

Answer 3

The easiest way is use map :

var depRefList: Array<Datable> = fetchDepRefs().map { $0 as Datable }
var depObsList: Array<Datable> = fetchDepObss().map { $0 as Datable }
var allDeps = (depRefList + depObsList)
            .sort { $0.date.timeIntervalSince1970 > $1.date.timeIntervalSince1970 }

since depRefList is [Datable] , and fetchDepRefs() is [DEPref] , Thay are different type, So it's neccecary to transfer [DEPref] to [Datable] , The map function will do this for you. The flowing code:

var depRefList: Array<Datable> = fetchDepRefs().map { $0 as Datable }

is equal to:

let depRefs: [DEPref] = fetchDepRefs()

var datables = [Datable]()

for depRef in depRefs {
    let datable = depRef as Datable
    datables.append(datable)
}

var depRefList: Array<Datable> = datables