为什么当参数为 int 时'cannot use ... as type uint8 in argument to ...'出现编译错误

Question

我是新手，正在解决GO编程语言中的问题。该代码应以随机的lissajous数字创建gif动画，并以 palate的不同颜色生成的图像：

。

// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// Run with "web" command-line argument for web server.
// See page 13.
//!+main
// Lissajous generates GIF animations of random Lissajous figures.
package main
import (
    "image"
    "image/color"
    "image/gif"
    "io"
    "math"
    "math/rand"
    "os"
)
//!-main
// Packages not needed by version in book.
import (
    "log"
    "net/http"
    "time"
)
//!+main
// #00ff55
var palette = []color.Color{color.RGBA{0x00, 0xff, 0x55, 0xFF}, color.Black, color.RGBA{0x00, 0x00, 0xff, 0xFF}, color.RGBA{0xff, 0x00, 0xff, 0xFF}}
const (
    whiteIndex = 0 // first color in palette
)
func main() {
    //!-main
    // The sequence of images is deterministic unless we seed
    // the pseudo-random number generator using the current time.
    // Thanks to Randall McPherson for pointing out the omission.
    rand.Seed(time.Now().UTC().UnixNano())
    if len(os.Args) > 1 && os.Args[1] == "web" {
        //!+http
        handler := func(w http.ResponseWriter, r *http.Request) {
            lissajous(w)
        }
        http.HandleFunc("/", handler)
        //!-http
        log.Fatal(http.ListenAndServe("localhost:8000", nil))
        return
    }
    //!+main
    lissajous(os.Stdout)
}
func lissajous(out io.Writer) {
    const (
        cycles  = 5     // number of complete x oscillator revolutions
        res     = 0.001 // angular resolution
        size    = 100   // image canvas covers [-size..+size]
        nframes = 64    // number of animation frames
        delay   = 8     // delay between frames in 10ms units
    )
    freq := rand.Float64() * 3.0 // relative frequency of y oscillator
    anim := gif.GIF{LoopCount: nframes}
    phase := 0.0 // phase difference
  colorIndex := 2
  for i := 0; i < nframes; i++ {
    rect := image.Rect(0, 0, 2*size+1, 2*size+1)
        img := image.NewPaletted(rect, palette)
        for t := 0.0; t < cycles*2*math.Pi; t += res {
            x := math.Sin(t)
            y := math.Sin(t*freq + phase)
      img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5), colorIndex)
      colorIndex++
        }
        phase += 0.1
        anim.Delay = append(anim.Delay, delay)
        anim.Image = append(anim.Image, img)
    }
    gif.EncodeAll(out, &anim) // NOTE: ignoring encoding errors
}
//!-main

这是我遇到的错误

lissajous/main.go:76: cannot use colorIndex (type int) as type uint8 in argument to img.SetColorIndex

INT和UINT8类型之间是否存在区别？

Answer 1

colorIndex的类型是int。参数类型是uint8。int不能分配给uint8。以下是修复程序的一些选择：

• 将colorIndex声明为未型常数。

  const colorIndex = 2
  

• 将colorIndex称为UINT8类型：

  colorIndex := uint8(3)
  

• 转换在通话中的值：

  img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5), uint8(colorIndex))
  

您可以用byte在此答案中替换uint8的所有用途，因为byte是uint8的别名。

Answer 2

在变量声明中，使用默认类型，在您的情况下， colorIndex := 2，即colorIndex变为int，而不是uint8。

来自文档（https://golang.org/ref/spec#short_variable_declarations）："如果存在类型，则给出每个变量。; ..."

" var i = 42//i是int"

，然后

"一个非类型的常数具有默认类型，该类型是在需要键入值的上下文中隐式转换的类型不是显式类型。非类型常数的默认类型分别为布尔，符文，int，float64，complex128或字符串，具体取决于它是布尔，符文，符文，整数，浮点，浮点，复杂或字符串常数。"

因此，要获得UINT8，您应该明确将ColorIndex声明为UINT8 var colorIndex uint8 = 2，或在IMG.SetColorIndex中施放UINT8 AS： img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5), uint8(colorIndex))