【Go Time】Go語言常量定義關鍵字const

1. 常量

   • 函數內定義常量

     func consts() {
           const filename = "abc.txt"
           const a, b = 3, 4
           var c int
           c = int(math.Sqrt(a*a + b*b))
           fmt.Println(filename, c)
     }

   • 包內定義常量

     package main
     const filename = "abc.txt"

   • const()定義

     const (
        filename = "abc.txt"
        a, b = 3, 4
     )

   • const數值，編譯器能夠推測變量類型

     const a, b = 3, 4
     var c int
     // 編譯器能夠推測變量類型
     c = int(math.Sqrt(a*a + b*b))

2. 枚舉

   • iota實現自增值

     const (
        cpp = iota
        _
        python
        golang
        javascript
     )
     fmt.Println(cpp,python,golang,javascript) // 0 2 3 4
     
     const (
        b = 1 << (10 * iota)
        kb
        mb
        gb
        tb
        pb
     )
     fmt.Println(b,kb,mb,gb,tb,pb) 
     // 1 1024 1048576 1073741824 1099511627776 1125899906842624