go -- Language Fundamentals

2020/02/23

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Main Concepts Data Type

1. 25个key words。变量命名以字母或下划线开头。但是不推荐_出现在中间。
2. 声明和赋值：
   ex：var name string = “darcy”
       var name string–声明 name = `darcy`–赋值
       var name = `darcy`
       var (
            name1 = “darcy”//没有";"
            name2 = “lizzy”
            )
       firstName := “darcy”–声明and赋值(推荐)；
       x,y,x := 1,2,3–多变量分别声明赋值
       x,y := y,x–exchange

go’s types	basic	aggregate	reference	interface
ex:	numbers,strings and booleans	arreys,structs	pointers,slices,maps,functions and channels	…

4. string中的"“和’’,``作用不同”/n/n"会被转义,``不会，而’'表示rune literal（码点字面量，类型int32）
5. string是immutable. 变量名仅相当于一个指针， 所以也不能进行修改（s[0]=‘a’ ,报错，但是s += 'a’可）
6. zero values:0,false,"",nil(for slice pointer map channel function.etc)
7. 词汇基础
   注释：// /* */
   key words:break default func if .etc
   operator and punctuation:+ - & += := .etc
   boolean type: true false
   numeric type:int int8 uint float32 complex64 byte rune .etc
   array type: [10] int []32 byte
   slice type:make([]int, 50, 100)
   struct type: struct{string name, int age}
8. operator orders:从上到下
   * / % << >> & &^
   + - | ^
   == != < <= > >=
   &&
   ||
   btw: &:bitwise AND
        |: bitwise OR
        ^: bitwise XOR
        &^: bit clear (AND NOT)
        <<: left shift【var x unit8 = 2;x = x << 1;fmt.Printf("%08b",x) 输出：00000100】
        >>: right shift
9. 输出变量(print verbs)：
   %v: struct
   %T: show type
   %d: uint int.etc
   %t: bool
   %g(%5.1f.etc ): float32 complex64 etc.
   %s: string
   %p: chan
   %pointer %P
   %b: 二进制表示
   %o: 八进制
   %x: 十六进制表示
   %q: []rune【fmt.Printf("%q", []rune(“nice”)) 输出：[‘n’,‘i’,‘c’,‘e’]】

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other things

1. fmt.Println(“good Day[5]”): 输出为D的ascii(68)
2. fmt.Printf("%3d %8b %08b", 2, 2, 2)输出：
     2       10 00000010
3. 和NaN作比较永远为false
4. s := “hello好”；fmt.Println(len(s));fmt.Printlin(utf8.RuneCountInString(s)) 输出：9和6
5. scope（作用域）：

type	local-level	global-level
scope	own block	file:lowercase:anywhere in the file;package:uppercase:anywhere within the package
lifetime	end of the enclosing block	the entire execution of the program

{}in the proceding code is called a “syntactic block”,一个{}即为一块（stack）
当然还有lexical block，包括explicit和implicit block

6. const (
   a = iota
   _
   b = iota
   );fmt.Printf("%d %d", a, b)
   输出：0 2