How can I convert a Kotlin lambda to a String and back to a lambda?

Question

How can I convert () -> Unit to a String and back to an executable method? From what I've seen so far lambdas in Kotlin are Serializables, which should be half way to the solution, but I cannot figure out how to make this conversion.

Answer 1

If the only constraint is that the result be a String, then you can actually serialize the instance of the function type to a byte array and convert it to a String in any way that will let you do the reverse, such as encode it with Base64.

Here's how you encode it:

val f: (Int) -> Int = { it * 2 }
val serialized = ByteArrayOutputStream().run {
    ObjectOutputStream(this).apply { writeObject(f) }
    toByteArray()
}
val string = Base64.getEncoder().encodeToString(serialized)

And here's how to decode it back:

val decoded = Base64.getDecoder().decode(string)

@Suppress("UNCHECKED_CAST")
val deserialized: (Int) -> Int =
    ObjectInputStream(ByteArrayInputStream(decoded))
        .readObject() as (Int) -> Int

Here's a complete runnable example: (link)

Note that for this to work, the side that decodes the string to a function instance must have the same class loaded for the lambda as the side that encoded it, as otherwise deserializing it will likely fail.