Go by Example: Constants and iota
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Go supports constants of character, string, boolean, and numeric values. We can use iota to simulate C’s enum or #define constant. |
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package main
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import (
"fmt"
"strconv"
)
import "math"
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const s string = "constant"
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Sepcial method to generate maximum of uint. Ref: http://blog.golang.org/constants |
const MaxUint = ^uint(0)
const MaxUint32 = ^uint32(0)
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Here we simulate C’s |
type Season uint8
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const (
Spring = Season(iota)
Summer
Autumn
Winner
)
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output function for Season variable |
func (s Season) String() string {
name := []string{"spring", "summer", "autumn", "winner"}
i := uint8(s)
switch {
case i <= uint8(Winner):
return name[i]
default:
return strconv.Itoa(int(i))
}
}
func main() {
fmt.Println(s)
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A |
const n = 500000000
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Constant expressions perform arithmetic with arbitrary precision. |
const d = 3e20 / n
fmt.Println(d)
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A numeric constant has no type until it’s given one, such as by an explicit cast. |
fmt.Println(int64(d))
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A number can be given a type by using it in a
context that requires one, such as a variable
assignment or function call. For example, here
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fmt.Println(math.Sin(n))
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Assign Season variable and print it |
s := Summer
fmt.Println(s)
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Assign invalid range Season variable and print it |
s = Season(9)
fmt.Println(s)
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fmt.Println(MaxUint)
fmt.Println(MaxUint32)
}
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$ go run constant.go
constant
6e+11
600000000000
-0.28470407323754404
summer
9
18446744073709551615
4294967295
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