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kotlinlang

<@U2E974ELT> the `copy` function is effectively a persister (read: local factory) function to make data classes persistent isn't it?

```
data class Thingy(val x: Double, val y: Int)

val first = Thingy(1.0, 42)
val second = first.copy(x = 2.0)
```

you dont get any sharing but you do get persistence.

groostav: The `copy` is great (better than nothing). but what if I want to set `x = 2.0` and update `y = 3.0`, but only if `someProperty` is true? With copy I have to write something like:
```
val second = first.copy(x = 2.0)
val third = if (someProperty) second else second.copy(y = 3.0)
```
or 
```
val second = first.copy(x = 2.0, y = if (someProperty) 3.0 else first.y)
```
The first approach is inefficient, and the second does not scale to conditional update of multiple properties. Neither is plesant nor clear.