[swift-evolution] [Pitch] Property reflection

[Austin Zheng]

Yes, it was pretty much meant as a KVC-like feature for Swift. Get a
reference to a property from a string which would allow you to get and set
its value.

On Fri, May 27, 2016 at 11:53 AM, Ricardo Parada <rparada at mac.com> wrote:

>
> On May 26, 2016, at 9:25 PM, Austin Zheng via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> ```
> myPerson.typedReadWriteProperty<Int>("age")?.set(30)
>
> try myPerson.allNamedProperties["age"]?.set(30)
> ```
>
>
> Can you elaborate on what this API would be used for?  KVC? For instance,
> I played with Mirror the other day and my code to get a value given the
> property name looked more like this:
>
> let age = myPerson.value(forKey:”age”) as! Int
>
> And this is what I did:
>
> // KVC stands for key-value-coding… but I only know how to get values.  I
> don’t know how to set values
>
> protocol KVC {
>    func value(forKey key: String) -> Any!
> }
>
> // Default implementation
> extension KVC {
>    func value(forKey key: String) -> Any! {
>        let aMirror = Mirror(reflecting:self)
>        for case let (label?, value) in aMirror.children {
>            if label == key {
>                return value
>            }
>        }
>        return nil
>    }
> }
>
> public struct Person : KVC {
>    let firstName: String
>    let lastName: String
>    let age: Int
>
>    func fullName() -> String {
>        return "\(firstName) \(lastName)"
>    }
> }
>
> let aPerson = Person(firstName:"John", lastName:"Doe", age:48)
>
> // It works for stored properties
> let lastName = aPerson.value(forKey:"lastName") as! String
> print("Last name is \(lastName)")
>
> // It does not work for instance methods, i.e. fullName is not a stored
> property
> let fullName = aPerson.value(forKey:"fullName")
> if fullName != nil {
>    print("Full name is \(fullName)")
> } else {
>    print("Unable to get fullName via KVC")
> }
>
>
>
>
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