考虑 F# 中的这段代码:
let n = 10000000
let arr = Array.init n (fun _ -> 0)
let rec buildList n acc i = if i = n then acc else buildList n (0::acc) (i + 1)
let lst = buildList n [] 0
let doNothing _ = ()
let incr x = x + 1
#time
arr |> Array.iter doNothing // this takes 14ms
arr |> Seq.iter doNothing // this takes 74ms
lst |> List.iter doNothing // this takes 19ms
lst |> Seq.iter doNothing // this takes 88ms
arr |> Array.map incr // this takes 33ms
arr |> Seq.map incr |> Seq.toArray // this takes 231ms!
lst |> List.map incr // this takes 753ms
lst |> Seq.map incr |> Seq.toList // this takes 2111ms!!!!
为什么模块上的iter
andmap
函数比和模块等效的函数Seq
慢得多?Array
List