有效地保留最后N个推送项目的集合

Question

Given:

1. slice with pre-known capacity
2. capacity and number of slices are large , and around 15MB of memory will be used, so I don't want to waste memory and want to keep minimum memory.
3. slice will be updated by removing first element and adding new element to end of slice.

b = append(b[1:], n) will increase capacity

to shift and assign myself, I wrote

func shiftAndPut(a []int, n int) (b []int) {
    b = make([]int, cap(a), cap(a))
    for i,v := range(a[1:]) {
        b[i] = v
    }
    b[len(b)-1] = n
    return
}

https://play.golang.org/p/7xIBh0UPp2w

It keeps the capacity same, but requires various computations

1. iterating slice one time,
2. calling of function,
3. new variable for small time,
4. sub slicing in range function, which adds more computations,
5. etc

Is there any more optimised way to do this?

Answer 1

Slice ring buffer, custom implementation :

data := make([]int, cap, cap)
pointer := 0

data[pointer] = newData
pointer = (pointer+1) % cap

custom/ring package implemetation :

data := ring.New(cap)
data.Value = newData
data = data.Next()

After suggestion in comment thread, I did benchmark between slice custom shifting and custom/ring

BenchmarkCustom1000-4         100000         17322 ns/op
BenchmarkRing1000-4           100000         22824 ns/op
BenchmarkCustom-4           100000000           17.4 ns/op
BenchmarkRing-4             100000000           22.8 ns/op

custom slice shifting using variable (pointer or flag) is faster and also memory optimised.