span-slice.fsx

#I @"C:\Users\Isaac\.nuget\packages"
#r @"Microsoft.NETCore.App\2.2.1\ref\netcoreapp2.2\netstandard.dll"
#r @"system.memory\4.5.2\lib\netstandard2.0\System.Memory.dll"
#r @"System.Runtime.CompilerServices.Unsafe\4.5.2\lib\netstandard2.0\System.Runtime.CompilerServices.Unsafe.dll"
#r "System.Runtime"

open System

let x = "Foobarbazbiz"

type Span<'T> with
    member inline this.GetSlice(startS, endS) =
        match (startS, endS) with
        | (None, None) -> this
        | (Some s, None) -> this.Slice s
        | (None, Some s) -> this.Slice(0, s + 1)
        | (Some a, Some b) -> this.Slice(a, (b - a + 1))

type ReadOnlySpan<'T> with
    member inline this.GetSlice(startS, endS) =
        match (startS, endS) with
        | (None, None) -> this
        | (Some s, None) -> this.Slice s
        | (None, Some s) -> this.Slice(0, s + 1)
        | (Some a, Some b) -> this.Slice(a, (b-a + 1))

let inline foo() =
    let z = x.AsSpan()
    z.[0..2]

let bar() =
    let z = x.AsSpan()
    z.Slice(0, 3)

let baz() =
    x.Substring(0, 3)

#time

// Real: 00:00:00.011, CPU: 00:00:00.015, GC gen0: 0, gen1: 0, gen2: 0
for _ in 1 .. 1000000 do
    let _ = foo()
    ()

// Real: 00:00:00.002, CPU: 00:00:00.015, GC gen0: 0, gen1: 0, gen2: 0
for _ in 1 .. 1000000 do
    let _ = bar()
    ()

// Real: 00:00:00.016, CPU: 00:00:00.015, GC gen0: 10, gen1: 0, gen2: 0
for _ in 1 .. 1000000 do
    let _ = baz()
    ()