Assignments as expressions


#1

Is there a discussion or rational to forbidding using an assignment as an expression in Kotlin?

I love the ability Kotin gives me write terse code, but this goes kind of contrary to that.

I understand the risks, but some countermeasure can be taken, like GCC that warns if you do if (x = 3) (in kotlin, only boolean variable would affected so if (x = true)).

Maybe this impacts smart casts?

There’s a discussion here, but I’m not really convinced – the cases mentioned in Micah’s last post seem quite frequent to me.

Simple recent example:

class Dechain<T> (var head: Chain<T>? = null, var tail: Chain<T>? = null)

    ...

    override fun pushFront(e: T)
        = if (head == null) {
            head = Chain(e, null, null)
            tail = head
        } else {
            head ?. prev = Chain(e, null, head)
            head = head ?. prev
        }

    // what I really wanted to write:
    override fun pushFront(e: T)
        = if (head == null) head = tail = Chain(e, null, null)
          else head = head ?. prev = Chain(e, null, head)

    ...

I’d even take a weird syntax (or less weird like :=) or even something that triggers warnings.

Edit: closest I can get, but not near as readable:

fun pushFront(e: T)
    = if (head == null) Chain(e, null, null).let { head = it ; tail = it }
      else Chain(e, null, head).let { head ?. prev = it ; head = it }

#2

Not going into philosophy of it, simple technical answer: the syntax for named arguments: foo(a = b) means “call foo with the parameter a having value b”.