Declaring var with Primitive Data Types
Primitive Data Types 指的是一些基本的数据类型，这些类型不依赖于其他类型，是构成更复杂的数据类型的基础
函数外的每个语句都必须以关键字开始(var, func 等等)
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| var num int
num = 11
fmt.Println(num)
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Esay to write way:
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| var num int = 11
var greeting string = "Hello"
fmt.Println(num, greeting)
// 如果初始化值已存在，则可以省略类型;变量会从初始值中获得类型
var i,j = 1,2
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在函数中，简洁赋值语句 := 可在类型明确的地方代替 var 声明。
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| num := 11
greeting := "Hello"
fmt.Println(num, greeting)
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declaring multiple vars at the same time
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| // Declare three integer variables named "x", "y", and "z" with initial values of 1, 2, and 3, respectively. GO简洁的特色！
x, y, z := 1, 2, 3
fmt.Println(x, y, z)
// var x, y, z int = 1, 2, 3
x, y, z := 1, "hello", true
fmt.Println(x, y, z)
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显示转换 and 类型推到
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| num := 11
float64 := float64(num)
// 隐式转换导致容易混淆
var i int
j := i // j is a int from i
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Pointers
Like in python, big and complex objects are natively pointer, like Slice, Map, Function. Small of simple objects are not, like int, bool, string, array.
Go has a interesting feature to expose this machenisim. For example, declare a var “prt” point to a string variable.
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| // 这里用 地址变量类型 *Type 声明 prt
var prt *string // *string is an example of type
fmt.Println(prt)
// <nil> This is an empty pointer, since prt has not been initiallized
var greeting string = "hello"
// 这里用 取址符 & 给 prt 赋值
prt = &greeting // & is "address operator".
fmt.Println(prt)
// 0xc0000741e0 address of greet var
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Using dereference operator in ‘*prt’ expression access the varlue of string var “greeting”.
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| *prt = "world" // * is dereference operator 取值符
fmt.Println(greeting)
// world - no longer hello
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However, if you haven’t initialize prt var, it’s going to fail.
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| var prt2 *string
*prt2 = "world"
fmt.Println(*prt2)
// panic: runtime error: invalid memory address or nil pointer dereference
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One way to fix it without create a string var is 使用new 函数创建一个新的变量，并返回其指针.
但是，该内存块并没有初始化，所以它返回的是该类型的零值，比如这里对于string类型，应该返回空格。
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| var prt2 *string = new(string)
*prt2 = "world" // 这里给地址变量prt取值后改变这个值
fmt.Println(*prt2)
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Go doesn’t allow pointer arithmetic
Since it is dangous