Access properties via subscripting in Swift

Question

I have a custom class in Swift and I\'d like to use subscripting to access its properties, is this possible?

What I want is something like this:

clas         


        

Answer 1

Shim's answer above doesn't work anymore in Swift 4. There are two things you should be aware of.

First of all, if you want to use value(forKey:) function, your class must inherit NSObject.

Secondly, since Objective-C doesn't know anything about value type, you have to put the @objc keyword in front of your value type properties and Swift will do the heavy-lifting for you.

Here is the example:

import Foundation

class Person: NSObject {
    @objc var name: String = "John Dow"
    @objc var age: Int = 25
    @objc var height: Int = 180

    subscript(key: String) -> Any? {
        return self.value(forKey: key)
    }
}

let person: Person = Person()

person["name"] // "John Dow"
person["age"] // 25
person["height"] // 180

Answer 2

I suppose you could do:

class User {
    let properties = Dictionary<String,String>()

    subscript(key: String) -> String? {
        return properties[key]
    }

    init(name: String, title: String) {
        properties["name"] = name
        properties["title"] = title
    }
}

Without knowing your use case I would strongly advise against doing this.

Another approach:

class User {
    var name : String
    var title : String

    subscript(key: String) -> String? {
        switch key {
            case "name" : return name
            case "title" : return title
            default : return nil
        }
    }

    init(name: String, title: String) {
        self.name = name
        self.title = title
    }
}

It might be worth noting that Swift doesn't appear to currently support reflection by names. The reflect function returns a Mirror whose subscript is Int based, not String based.

Answer 3

Adding some syntax sugar to Benzi's answer:

protocol PropertyReflectable { }

extension PropertyReflectable {
    subscript(key: String) -> Any? {
        let m = Mirror(reflecting: self)
        return m.children.first { $0.label == key }?.value
    }
}

struct Person {
    let name: String
    let age: Int
}

extension Person : PropertyReflectable {}

Then create a Person and access it's keyed properties.

let p = Person(name: "John Doe", age: 18)

p["name"] // gives "John Doe"
p["age"] // gives 18

Answer 4

This is a bit of a hack using reflection. Something along the lines of the following could be used.

protocol PropertyReflectable { }

extension PropertyReflectable {
    subscript(key: String) -> Any? {
        let m = Mirror(reflecting: self)
        for child in m.children {
            if child.label == key { return child.value }
        }
        return nil
    }
}

struct Person {
    let name: String
    let age: Int
}

extension Person : PropertyReflectable {}

Then create a Person and access it's keyed properties.

let p = Person(name: "John Doe", age: 18)

p["name"] // gives "John Doe"
p["age"] // gives 18

You could modify the subscript to always return an interpolated string of the property value.

Answer 5

Using valueForKey should enable you to access properties using their names. Be sure that you're working with a object that inherit NSObject

class people: NSObject {
    var age: NSString = "44"
    var height: NSString = "153"
}

let person:people = people()

let stringVariable = "age"

person.valueForKey("age")
// Print "44"

person.valueForKey("\(stringVariable)")
// Print "44"

Answer 6

(GRMustache author here)

Until a swift-oriented Mustache library is out, I suggest having your classes inherit from NSObject (so that they have the valueForKey: method). GRMustache will then fetch values with this method.

In case this would still not work (blank values in the rendering), you may try to disable GRMustache security features (see https://github.com/groue/GRMustache/blob/master/Guides/security.md#disabling-safe-key-access)

Should you experience any other trouble, please open an issue right into the repository: https://github.com/groue/GRMustache/issues

EDIT February 2, 2015: GRMustache.swift is out: http://github.com/groue/GRMustache.swift