Assignment not allow in while expression?

61

It is a lot cleaner and expressive. Thanks.

62

For code that allows it, by having null as breaking return value, i really prefer generateSequence - it generates an infinite sequence terminated should nextFunction return null.

Code for the reader could be written as:

generateSequence { reader.readLine() }.forEach { println(it) }

The drawback of this solution is however that the code itself is not really speaking.

Should a condition other than === null be required, takeIf or takeUnless could be used:

generateSequence(0) { (it + 2).takeUnless { n -> n > 15 } }.forEach { println(it) }
3 Likes
63

This right here. I keep running into this issue.

64

Yup, this is not at all uncommon to me.
Consuming a paginated feed or result set is the repeat offender.
while(true) + if/break works fine and doesn’t take much work, but just feels dirty in a language otherwise so elegant. The condition should be part of the loop statement, dammit.
var + duplicated assignment is even worse.

Sure, you can (sometimes) wrap it as a sequence or something, but it feels so unneccessary for a really quite simple bit of looping logic.

65

I am firmly in the ‘this should be allowed’ side of the debate.

Here is a use case for you that is very critical for my application:

if( (a=(… some expensive evaluation))>0 && (b=(… some expensive evaluation))>0){

… Do something with ‘a’ and ‘b’

}

For example, the expensive evaluation above is a JPA or SQL query. Notice the nuance: second evaluation wont be executed unless first returned valid value, so executing this upfront would be slower.

Another observation: The solution of using lambda does not property address nullability check.
The code below fails with ‘Variable ‘x’ must be initialized’:

var x:Any?;
{x="hello"}()   
println(x.toString());