Golang slice usage

Golang is an open source programming language that has been widely used in the Internet and big data fields since its release in 2007. Among them, slice (slice), as a dynamic array feature, has become one of the most practical data structures in Golang.

This article will introduce in detail the usage of slices in Golang in terms of definition, creation, interception, expansion, and the difference from arrays.

1. Definition of slice

Slice in Golang is a reference type data structure. It is an encapsulation of the underlying array and contains the reference, length and Capacity and other related information.

The definition format of a slice is: var name []Type, where name is the name of the slice and Type is the type of the slice element.

For example:

var s []int // Define an empty slice of type int
var a []string // Define an empty slice of type string

2. Creation of slices

Slices can be created through the make function. The format of the make function is make([]Type, length, capacity), where Type is the type of the slice element, length is the length of the slice, and capacity is the capacity of the slice.

For example:

s := make([]int, 3, 5) // Create an int type slice with a length of 3 and a capacity of 5
a := make( []string, 2) //Create a string type slice with length 2 and capacity 2

It should be noted that if the capacity is not specified, the capacity of the created slice will be equal to its length, that is: make([]Type, length).

In addition, slices can also be created through arrays. For example:

arr := [5]int{1, 2, 3, 4, 5}
s := arr[1:3] // Create an underlying array from subscript 1 to Slice with subscript 2

3. Slice interception

A slice can be intercepted to obtain a new slice. The intercepted format is name[start:end], where start represents the start. Subscript, end represents the end subscript (excluding end itself).

It should be noted that the value range of start and end is within [0, len(name)], and start≤end.

For example:

s := make([]int, 5) // Create an int type slice with a length of 5
s1 := s[1:3] // Get the slice from subscript 1 to subscript 2

In addition, you can also omit any one or both of start or end, so that the slice will select the maximum or minimum value as the corresponding start or end by default.

For example:

s := make([]int, 5) // Create an int type slice of length 5
s1 := s[:3] // Get Slice from subscript 0 to subscript 2
s2 := s[2:] // Get the slice from subscript 2 to subscript 4
s3 := s[:] // Get the entire slice

4. Expansion of slices

The expansion of slices means that when the length of the original slice is not enough, it is necessary to increase the capacity of the slice, and at the same time, re-open a larger underlying array and add the data in the original array. The data is copied to the new underlying array.

The mechanism of slicing expansion in Golang is to first apply for a continuous memory with a larger capacity than the current slice, and then copy the data in the original underlying array to the new underlying array. Finally, the original underlying array is released, allowing the original slice to reference the new underlying array.

The expansion process of slices is implemented at the bottom by the runtime library. This also explains why when using slices, you need to use the make function to specify the capacity (when the capacity is insufficient, it will be expanded), or in the slice. Declare it within the scope.

It should be noted that when a slice is expanded, a memory space will be allocated. If the elements in the slice are no longer useful, it is recommended to avoid keeping these useless elements in the slice, which will lead to excessive occupation. of memory.

5. The difference between slices and arrays

In Golang, arrays and slices are two different data types. On the one hand, an array is a container with a fixed length that stores elements of the same type, while a slice is a dynamic array (dynamic container); on the other hand, when an array is used, its length is already determined when it is defined, and The length of the slice can be changed dynamically at runtime;

For arrays, the length is a component of the array type and cannot be changed, and when using an array, the length of the array needs to be clearly given. In many cases, using arrays can bring a lot of inconveniences, such as when a large amount of data needs to be processed, the array may take up too much memory space and cause the program to crash.

On the other hand, slices are a very useful data structure. Due to its dynamically scalable nature, slicing can well overcome the shortcoming of the fixed length of an array and is one of the preferred data types when dealing with variable-sized data collections. When using it, we can first declare an empty slice and then dynamically increase its length according to actual needs.

Conclusion

This article mainly introduces the common usage of slices in Golang such as definition, creation, interception, expansion, and the difference from arrays. As one of the powerful data structures in Golang, slicing can help us process variable-sized data collections quickly and easily. Mastering the operation method of slicing allows us to write Golang programs more efficiently.

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