Golang slice underlying implementation

Golang is an efficient development language. When processing large amounts of data, using slices is a very common way. Slicing is widely used in Golang, and the underlying implementation principles are often asked in interviews. This article will delve into the underlying implementation of Golang slicing.

1. Definition of Golang slice

In Golang, slice is a data structure of dynamic array. It is a pointer to the underlying array and records the length and capacity of the slice. We can use the make() function to create slices.

For example:

a := make([]int, 5) //长度为5，容量为5
b := make([]int, 5, 10) //长度为5，容量为10

where a is a slice with the same length and capacity, and b is a slice with a length of 5 and a capacity of 10.

2. The underlying structure of the slice

The underlying structure of the slice contains three attributes: pointer, length and capacity.

type slice struct {
    ptr uintptr //指针
    len int //长度
    cap int //容量
}

The pointer points to the first element of the underlying array, the length represents the number of elements in the slice, and the capacity represents the number of elements that can be stored in the underlying array.

3. Slice expansion

Slice expansion is a dynamic process. When the length of the slice exceeds its capacity, Golang will reallocate a larger memory and copy the original data to the new memory space.

For example, when a new element is added to a slice with a length of 10 and a capacity of 10, its capacity will be expanded to 20, and all original elements will also be copied to the bottom of the new 20 elements. in the array.

The expansion of slices is a relatively time-consuming operation, so when using slices, we try to estimate the number of elements that need to be stored.

4. Shared underlying array of slices

When two slices share the same underlying array, the operations between them will affect each other.

For example:

a := []int{1, 2, 3, 4, 5, 6}
b := a[1:4] //切片
b[0] = 100
fmt.Println(a) //[1 100 3 4 5 6]
fmt.Println(b) //[100 3 4]

In the above code, slice b shares the underlying array of a, so when we modify the elements in b, the corresponding elements in a will also be modified.

5. Slice pointer

The slice itself is a pointer to the underlying array, so we can use the pointer to the slice to operate the slice.

For example:

a := []int{1, 2, 3, 4, 5}
b := &a
fmt.Println(*b) //[1 2 3 4 5]
(*b)[0] = 100
fmt.Println(a) //[100 2 3 4 5]

In the above code, b is a pointer to a slice, we can get the element value of a through b. At the same time, elements in a can be modified through b.

6. Notes on using slices

You need to pay attention to the following points when using slices:

(1) When slices are passed as function parameters, Changes to the slice inside the function will affect the slice outside the function.

(2) When a slice shares an underlying array, modifying the value of an element within the slice will affect other slices sharing the underlying array.

(3) When the length and capacity of the slice are the same, a larger memory will be reallocated when the slice is expanded. Therefore, when using slicing, try to plan based on the estimated number of elements to avoid excessive expansion operations.

7. Summary

In this article, we have an in-depth discussion of the underlying implementation principles of Golang slicing, including the definition, underlying structure and expansion mechanism of slicing. At the same time, we also introduced slice pointers, shared underlying arrays and usage precautions. Understanding the underlying implementation principles of Golang slicing is of great significance for a deep understanding of the internal mechanism and implementation principles of the Golang language. When using slicing, you must keep in mind the underlying implementation principles of slicing to avoid potential performance issues and errors.

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