How to copy golang slice

#Golang's slice is a pointer structure pointing to the underlying array.

This structure has three attributes, 1. Pointer to the array, 2.len: the number of elements in the slice 3.cap: the amount of memory occupied by the slice.

Only by deeply understanding these three attributes can you avoid making mistakes when using slice. (Recommended learning: go)

Correctly understand variables and sharing

Multiple slices can share underlying data and reference arrays Some intervals may overlap

The above is a sentence from the golang Bible. A deep understanding of this sentence is very meaningful for schedule programming.

When shared data will be modified by other variables

func f1()  {
    a1 := []int{1,2,3,4,5,6}
    a2 := a1
    a3 := a1[1:3]
    a1[1] = 999
    
    fmt.Println("a1=",a1,"a2=",a2,"a3=",a3)
}

Running results

a1= [1 999 3 4 5 6] a2= [1 999 3 4 5 6] a3= [999 3]
Process finished with exit code 0

We clearly see the data sharing , a1 is modified at this time, both variables are modified

When will it not be modified

func f2()  {
    a1 := []int{1,2,3,4,5,6}
    a2 := a1
    a3 := a1[1:3]
    a2 = append(a2,888)
    a1[1] = 999
    fmt.Println("a1=",a1,"a2=",a2,"a3=",a3)
}

Running result

a1= [1 999 3 4 5 6] a2= [1 2 3 4 5 6 888] a3= [999 3]
Process finished with exit code 0

Although a1 is modified, a2 is not modified. We know that the append function will face memory reallocation. So when a2 appends, it will re-apply for memory space, copy the original array and add the new value. That is, when the append operation occurs, a2 no longer shares memory with a1.

When copying a slice, if you face multiple variables pointing to an array at the same time, you must consider data sharing and memory reallocation.

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