what is a kotliny way to generate a list of elemen...

# announcements

[projectmoon]

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

[pavi2410]

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

[nkiesel]

List<Int>(5) { it + 1 } (or it, not sure if that Ruby code starts with 0 or 1

[pavi2410]

For fun, I wrote a benchmark test here: https://pl.kotl.in/7GiATHz0A

The results are interesting 😯

[Mike]

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...

[Casey Brooks]

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

[nkiesel]

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.

[pavi2410]

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