what is a kotliny way to generate a list of elements given a number of elements? e.g. something like

5.times |x| mylist << x

in ruby

(1..5).forEach { num -> }

?

List<Int>(5) { it + 1 }

(or

it

, not sure if that Ruby code starts with

0

or

1

For fun, I wrote a benchmark test here: https://pl.kotl.in/7GiATHz0A The results are interesting 😯

Assuming you got similar results (1000, List<Int>(1000) much faster, 1M-> forEach much faster), then definitely agree. I think we'd all intuitively expect one or the other to be faster...

Another thing to consider is memory usage.

(1..5).forEach {  }

does not keep the entire list in-memory, it is just an iterator, so larger ranges do not take up more memory.

List<Int>(5) {  }

holds all elements in memory, and thus cannot be used for really large ranges

for starters, you should really use

nanoTime

for micro-benchmarks like this. Not because of the granularity but because that really measures the time the JVM was running instead of elapsed system time. But more to the point, the 2 do something very different: the

repeat

calls a block

n

times and throws away the returned values while the

List(n) { block }

keeps all the values. So why are we comparing the 2? I could see to compare

forEach

with

repeat

or a

for

loop.

Repeat wins over range! https://pl.kotl.in/Q3kaqNlTt