要点

• var用来定义一个变量
• 可以用:=这种shorter的方式，此时不用var
• const定义常量
• var/const (…)用来定义一组变量或常量
• 作用域同C/C++/Java等语法

变量声明&赋值

package main
import "fmt" // Printf()

/*
D:\examples>go run helloworld.go
Hello, world!
y - Hello world!
z - Hello world!
string a
string b
Hello, world! 1234567
y - Hello world! 1234567

D:\examples>
*/
func main() {
    // <<Introducing Go>> Page 19: 
    // May look strange to experienced Go programmers.
    var x string = "Hello, world!" 

    var y string
    y = "y - Hello world!"

    z := "z - Hello world!"

    var ( // Attention Pls: Here is not '{'!
        a = "string a"
        b = "string b"
    )

    fmt.Println(x)
    fmt.Println(y)
    fmt.Println(z)
    fmt.Println(a)
    fmt.Println(b)

    x = x + " 1234567"
    fmt.Println(x)

    y += " 1234567"
    fmt.Println(y)

    //a = 2 //cannot use 2 (type int) as type string in assignment
}

变量名

以字母开头，后面可以跟字母、数字、下划线。建议用camelCase风格。

作用范围

package main
import "fmt" // Printf()

var global_x = "Hello, world!"

func main() {
    var x string = "Hello, world!" 

    fmt.Println(global_x)
    fmt.Println(x)

    foo();
}

func foo() {
    fmt.Println("foo():", global_x)
    //fmt.Println("foo():", x) //undefined: x
}

再一例：

package main 

import "fmt"

var x int 

func print(x int) {
    fmt.Println("x = ", x)
}

/*
$ go run main.go
x =  100
x =  200
x =  101
$
*/
func main() {
    foo()
    print(x)

    x++ // x = 101

    bar()

    print(x)
}

func foo() {
    x = 100 // global variable 'x'
}

func bar() {
    x := 200 // local variable 'x'
    print(x)
}

常量

package main
import "fmt" // Printf()

func main() {
    const x string = "Hello, world!" 
    //x = "Another value" // cannot assign to x

    fmt.Println(x)
}