Is there an equivalent of Ruby's instance_eval in Swift? - swift

Question

In ruby I can pass a block into a method and have the block evaluated in the context of the receiving object.
class Receiver
def method_a
puts "hello from method_a"
end
def method_b
puts "hello from method_b"
end
def define_something &action
method_a
instance_eval &action
end
end
thing = Receiver.new
thing.define_something { method_b }
which produces the following output:
hello from method_a
hello from method_b
Whats the right way to implement something like this in Swift?
Here is what I have, but of course Xcode complains that methodB is an unresolved identifier.
class Receiver {
func methodA() {
print("hello from method A")
}
func methodB() {
print("hello from method B")
}
func defineSomething( action: () -> Void ) {
methodA()
action()
}
}
let thing = Receiver()
thing.defineSomething { methodB() }
BTW, this can also be done in Kotlin which has the idea of a function type with a receiver.
for example the following produces similar output to what the ruby example produces.
class Receiver {
fun methodA() = println("hello from methodA")
fun methodB() = println("hello from methodB")
fun defineSomething( action: Receiver.() -> Unit) {
methodA()
action()
}
}
fun main(args: Array<String>) {
val thing = Receiver()
thing.defineSomething { methodB() }
}
hello from methodA
hello from methodB

Answer 1

I don't know of a way to do that in the language. You can do it manually by having action take a Receiver instance as input, and then call action(self) inside of defineSomething(action:).
class Receiver {
func methodA() {
print("hello from method A")
}
func methodB() {
print("hello from method B")
}
func defineSomething(action: (_: Receiver) -> Void ) {
methodA()
action(self)
}
}
let thing = Receiver()
thing.defineSomething { $0.methodB() }
hello from method A
hello from method B