[io-2] Conceptual design for IO format

Here are some thoughts about IO format functionality I would like to add as soon as IO-2 is out. The idea is that we can add an easy way to write objects to streams and read them from streams. The resulting API could then simplify the work with serialization and file IO.

The idea is shown in the following example (using io-1 API):

interface IOFormat<T : Any> {
    fun Output.writeThis(obj: T)
    fun Input.readThis(): T
}

fun <T : Any> Input.readWith(format: IOFormat<T>): T = format.run { readThis() }
fun <T : Any> Output.readWith(format: IOFormat<T>, obj: T) = format.run { writeThis(obj) }

class ListIOFormat<T : Any>(val format: IOFormat<T>) : IOFormat<List<T>> {
    override fun Output.writeThis(obj: List<T>) {
        writeInt(obj.size)
        format.run {
            obj.forEach {
                writeThis(it)
            }
        }
    }

    override fun Input.readThis(): List<T> {
        val size = readInt()
        return format.run {
            List(size) { readThis() }
        }
    }
}

val <T: Any> IOFormat<T>.list get() = ListIOFormat(this)

IOFormat represents a way to read and write data with Input and Output. One can construct a format for complex objects from the formats of individual parts. It could be probably used as a way to customize serialization backends. The similar idea is currently used in kmath in-memory operations on data: https://github.com/mipt-npm/kmath/blob/dev/kmath-memory/src/commonMain/kotlin/scientifik/memory/MemorySpec.kt.

[fvasco]

Hi @altavir, the readThis() and writeThis(obj) functions look confusing to me, I propose something like readObject and writeObject, similar to readInt and writeInt.

Moreover I don’t understand why IOFormat interface contains only extension methods, do you wish to use it as an implicit parameter?

with (output) {
 with (UserFormat) {
  with (BookFormat) {
   write (user)
   write (book)
  }
 }
}

In closing, I wish understand why should this feature be included in this library, serialization libraries already perform this task (see kotlinx.serialization as example).

[fvasco]

I’ve replaced writeThis by writeObject. It looks more concise.

Please think twice about motivation. this has a special meaning in Kotlin.

maybe two small extensions for lists and maps

So my disapproval is still valid.