The difference between 'var' and ':=' in golang

There are many ways to define variables in the Go language.

Using the var keyword is the most basic way to define variables in Go. Sometimes := is also used to define variables.

Define variables

// 定义一个名称为“variableName”，类型为"type"的变量
// var variableName type
var number int

Define variables and initialize values

// 初始化“variableName”的变量为“value”值，类型是“type”
// var variableName type = value
var number int = 10

Initialize multiple variables at the same time, also called Parallel assignment

/*
    定义三个类型都是"type"的变量,并且分别初始化为相应的值
    vname1为v1，vname2为v2，vname3为v3
*/
// var vname1, vname2, vname3 type = v1, v2, v3
var number1, number2, number3 int = 1, 2, 3

Do you think the above definition is a bit cumbersome? It doesn't matter, because the designers of the Go language also discovered that there is a way to make it simpler. We can directly ignore the type declaration, then the above code becomes like this:

/*    
定义三个变量，它们分别初始化为相应的值    
vname1为v1，vname2为v2，vname3为v3    
然后Go会根据其相应值的类型来帮你初始化它们
*/
// var vname1, vname2, vname3 = v1, v2, v3
var number1, number2, number3 = 1, 2, 3

Do you think the above is still a bit cumbersome? Okay, I think so too. Let’s continue simplifying:

/*    
定义三个变量，它们分别初始化为相应的值    
vname1为v1，vname2为v2，vname3为v3    
编译器会根据初始化的值自动推导出相应的类型*/
// vname1, vname2, vname3 := v1, v2, v3
number1, number2, number3 := 1, 2, 3

Doesn’t it look very simple now? := This symbol directly replaces var and type. This form is called a short statement. However, it has a limitation, that is, it can only be used inside a function; if used outside the function, it will not be compiled, so the var method is generally used to define global variables.

In other words, ":=" can only be used when declaring "local variables", while "var" does not have this restriction.

Recommended related articles and tutorials: golang tutorial

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