How to write complex Kotlin for loop

Question

It's easy to write simple loops like for (i in 0..10), but how to write more complex loops like:

for (byte i = 1 << 7; i != 0; i >>= 1)

or

for (byte i = 0x01; i != 0; i <<= 1)

Thanks for your help.

Michael Piefel · Accepted Answer · 2019-09-09 09:29:23Z

4

This is not what a for loop is for in Kotlin. You can use a normal while statement instead.

var i: Int = 1 shl 7
while (i != 0) {
    // . . .
    i = i shr 1
}

answered Sep 9, 2019 at 9:29

Michael Piefel

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Comments

Roland · Accepted Answer · 2019-09-09 11:21:19Z

2

In case you don't like having a var and are ok with using a Sequence, you could also use something like generateSequence instead, e.g.:

generateSequence(1 shl 7) {
  it shr 1
}
    .takeWhile { it != 0 }
    .forEach { ... }

// or: generateSequence(1 shl 7) { (it shr 1).takeIf { it != 0 } }.forEach { ... }

Otherwise Michaels answer about using while is perfectly fine.

answered Sep 9, 2019 at 11:21

Roland

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2 Comments

Michael Piefel Over a year ago

I like avoiding vars and find myself using that style more and more (and sadly Java is quite bad at it). However, I guess for simple loops I will continue the old-fashioned way.

Roland Over a year ago

@MichaelPiefel I tend to use it nearly everywhere now... I really like that seed, next-value-function and loop-termination-condition are so near by each other... (maybe I also just saw for (seed; next-value-function; loop-termination-condition)-statements too often, so that I think I need this construct ;-)

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