Say I have a list of size 30k elements, and I would like to perform an operation on all possible pairs within a list. So I had:
list.asSequence().flatMap { i ->
list.asSequence().map { j -> /* perform operation here */ }
}
Question 1:
我还注意到，这个flatMap-map操作比命令式循环版本要慢得多.(可能是因为关闭？)
for(i in list){
for(j in list){
}
}
Question 2:有没有办法提高flatMap/map版本的性能？
Answering to the question 2, we're considering to add flatMap overload which doesn't create closures for each element in the outer collection/sequence: https://youtrack.jetbrains.com/issue/KT-8602
But in case if you want to perform some side effects on each pair, rather than transforming the sequence, I'd advice to stick with for-loops or inlined forEach lambdas, which is effectively the same.