What is the usage of make in go language?

The function of make in the Go language is to allocate memory for slice, map, and channel and return an initialized value. Its usage methods are: 1. [make(map[string]string)]; 2. [make( []int, 2)]; 3. [make([]int, 2, 4].

The operating environment of this article: Windows7 system, Go1.11.2 , Dell G3 computer.

Recommendation: 《golang tutorial》

Usage of make in golang

Golang allocates memory mainly There are built-in functions new and make. Today we will explore how make can be played.

make can only allocate memory for slice, map, and channel, and return an initialized value. First, let’s take a look at the following three functions of make Different usages:

1. make(map[string]string)

2. make([]int, 2)

3. make([]int , 2, 4)

1. The first usage is to pass parameters that lack length and only pass the type. This usage can only be used in scenarios where the type is map or chan, for example make([]int) will report an error. The space length returned in this way defaults to 0.

2. The second usage specifies the length, for example, make([]int, 2) returns is a slice of length 2

3. In the third usage, the second parameter specifies the length of the slice, and the third parameter is used to specify the length of reserved space, such as a := make ([]int, 2, 4), it is worth noting here that the total length of the returned slice a is 4. The reserved does not mean the additional length of 4, but actually includes the number of the previous two slices. . So for example, when you use a := make([]int, 4, 2) like this, a syntax error will be reported.

Therefore, when we allocate memory for slice, we should Try to estimate the possible maximum length of the slice, and reserve memory space for the slice by passing the third parameter to make. This can avoid the overhead caused by secondary allocation of memory and greatly improve the performance of the program.

Summary:

make is only used to allocate and initialize data of types slice, map, and chan. new can allocate any type of data.

new allocation What is returned is a pointer, that is, type *Type. make returns a reference, that is, Type.

The space allocated by new is cleared, and after make allocates the space, it will be initialized.

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