escape analysis is eliminating the allocation in the simplification. in
reality the slice is stored in a persistent struct.
On Sun, Mar 1, 2020 at 8:50 AM <so.peter...@gmail.com> wrote:
> Jason,
>
> Your example does not appear to support your claim.
>
> A benchmark:
>
> package main
>
> import (
> "strconv"
> "testing"
> )
>
> type A struct {
> B string
> }
>
> func mycode(slice []A) {
> slice = slice[1:]
> }
>
> func BenchmarkMycode(b *testing.B) {
> a := make([]A, 256)
> for i := range a {
> a[i].B = "B: " + strconv.Itoa(i*cap(a))
> }
> b.ResetTimer()
> for N := 0; N < b.N; N++ {
> mycode(a)
> }
> }
>
> Output:
>
> $ go version
> go version go1.14 linux/amd64
> $ go test mycode_test.go -bench=. -benchmem
> BenchmarkMycode-4 1000000000 0.290 ns/op 0 B/op 0 allocs/op
>
> Peter
>
> On Saturday, February 29, 2020 at 6:53:18 PM UTC-5, Jason E. Aten wrote:
>>
>> Profiling suggests that reslicing to remove the first element of a slice
>> is doing alot of allocation; for instance in mycode() below.
>> This is surprising to me.... How could this be? is there anything I can
>> do about it?
>>
>> e.g.
>>
>> type A struct{
>> B string
>> }
>>
>> func mycode(slice []A) {
>> slice = slice[1:]
>> }
>>
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