Generic Type

[AhmedZahraz]

Hi, I'im trying to parse jsonString to an object that contains a generic type but it's not working. This is my example :

public class A: EVObject {

var test : String = ""
var test2 : String = ""
var data: T? = nil

}

public class B: EVObject {
var test3 : String = "" var test4 : String = ""
}

[evermeer]

This looks like a swift bug / missing feature where there is no workaround possible. I created a unit test for this. I will do some more tests and then push this test to github. Maybe you can confirm that the test that I created is how you wanted to use generics?

The problem is that a generic class is not key value coding complient. So it's not possible to set any of the properties using yourObject.setValue(value, forKey: key) Then for some reason it's also not executing the setValue forUndefinedKey on the object itself. When adding a base class with a setValue forUndefinedKey, then the calls will come in there.

I will create an Apple bug report for this.

class Workarounds2Tests: XCTestCase {
    func testGenerics() {
        let json:String = "{\"test\":\"test\", \"data\":\"data\"}"
        let a = A<NSString>(json:json)
        XCTAssertEqual(a.test, "test", "test should contin test")
        XCTAssertEqual(a.data as! String, "data ", "data should contin data")
    }
}

public class A<T where T:NSObject>: GenericsBase {
    var test : String = ""
    var data: T = T()

    // Handling the setting of non key-value coding compliant properties
    override public func setValue(value: AnyObject!, forUndefinedKey key: String) {
        switch key {
        case "test":
            test = value as! String
        case "data":
            data = value as! T
        default:
            println("---> setValue for key '\(key)' should be handled.")            
        }
    }
}

public class GenericsBase: EVObject {
    override public func setValue(value: AnyObject!, forUndefinedKey key: String) {
        println("---> GenericsBase: setValue for key '\(key)' should be handled.")
    }
}

[evermeer]

Unit test can be found at: https://github.com/evermeer/EVReflection/blob/master/EVReflection/EVReflectionTests/SwiftGenericsBug.swift

An Apple bug report has been posted with the ID 22218794

[evermeer]

I succeeded creating a workaround for this. I will push an update later today. For solving this issue you will get code like this:

class WorkaroundSwiftGenericsTests: XCTestCase {
    func testGenerics() {
        let json:String = "{\"test\":\"test\", \"data\":\"data\"}"
        let a = MyGenericObject<NSString>(json: json)
        XCTAssertEqual(a.test, "test", "test should contin test")
        XCTAssertEqual(a.data as! String, "data", "data should contin data")
    }
}

// Only put the generic properties in this class. put the rest in a base class
public class MyGenericObject<T where T:NSObject>: MyGenericBase, EVGenericsKVC {
    var data: T = T()

    public func genericSetValue(value: AnyObject, forKey key: String) {
        switch key {
        case "data":
            data = value as! T
        default:
            println("---> setValue '\(value)' for key '\(key)' should be handled.")
        }
    }
}

// Put the rest of the properties in a base class like this. Otherwise you have to handle each in the genericSetValue
public class MyGenericBase: EVObject {
    var test : String = ""
}

[evermeer]

I have pushed the update to GitHub. You have to use version 2.5.1 if you want to implement this workaround.

[evermeer]

i have renamed the method in the protocol. Now instead of implementing genericSetValue you can use override public func setValue(value: AnyObject!, forUndefinedKey key: String) { So now it's the same as the other situations where key value coding is not supported.

[evermeer]

Since this is a Swift limitation / bug and there is a workaround which is added as a unit test, I am closing this issue.

[AhmedZahraz]

Thanks @evermeer it's working now !