Go Tour，Excercise：切片索引超出範圍

Question

我正在通過Go語言遊的練習中工作，並且遇到了一個我無法弄清楚的障礙。我在做Exercise: Slices和我收到此錯誤：

256 x 256 

panic: runtime error: index out of range 

goroutine 1 [running]: 
main.Pic(0x10000000100, 0x3, 0x417062, 0x4abf70) 
    /tmpfs/gosandbox-08a27793_4ffc9f4a_3b917355_ef23793d_c15d58cc/prog.go:9 +0xa0 
tour/pic.Show(0x400c00, 0x40caa2) 
    go/src/pkg/tour/pic/pic.go:20 +0x2d 
main.main() 
    /tmpfs/gosandbox-08a27793_4ffc9f4a_3b917355_ef23793d_c15d58cc/prog.go:20 +0x25 

這裏是我的代碼：

package main 

import "tour/pic" 

func Pic(dx, dy int) [][]uint8 { 
    fmt.Printf("%d x %d\n\n", dx, dy) 

pixels := make([][]uint8, 0, dy) 

for y := 0; y < dy; y++ { 
    pixels[y] = make([]uint8, 0, dx) 

    for x := 0; x < dx; x++ { 
     pixels[y][x] = uint8(x*y) 
    } 
} 

return pixels 
} 

func main() { 
    pic.Show(Pic) 
} 

對於我的生活，我不能找到問題！

Answer 1

Slices

For a string, array, pointer to array, or slice a, the primary expression

a[low : high]

constructs a substring or slice. The index expressions low and high select which elements appear in the result. The result has indexes starting at 0 and length equal to high - low.

For arrays or strings, the indexes low and high must satisfy 0 <= low <= high <= length; for slices, the upper bound is the capacity rather than the length.

Indexes

A primary expression of the form

a[x]

denotes the element of the array, slice, string or map a indexed by x. The value x is called the index or map key, respectively. The following rules apply:

For a of type A or *A where A is an array type, or for a of type S where S is a slice type:

x must be an integer value and 0 <= x < len(a) 

a[x] is the array element at index x and the type of a[x] is 
the element type of A 

if a is nil or if the index x is out of range, a run-time panic occurs 

Making slices, maps and channels

make(T, n)  slice  slice of type T with length n and capacity n 
make(T, n, m) slice  slice of type T with length n and capacity m 

y必須是一個整數值和0 < = Y < LEN（像素[] UINT8）。 x必須是一個整數值並且0 < = x < len（pixel [] [] uint8）。例如，

package main 

import "tour/pic" 

func Pic(dx, dy int) [][]uint8 { 
    pixels := make([][]uint8, dy) 
    for y := 0; y < dy; y++ { 
     pixels[y] = make([]uint8, dx) 
     for x := 0; x < dx; x++ { 
      pixels[y][x] = uint8(x * y) 
     } 
    } 
    return pixels 
} 

func main() { 
    pic.Show(Pic) 
} 

Answer 2

package main 

import "tour/pic" 

func Pic(dx, dy int) [][]uint8 { 
fmt.Printf("%d x %d\n\n", dx, dy) 

    pixels := make([][]uint8, 0, dy) 

     for y := 0; y < dy; y++ { 
    // pixels[y] = make([]uint8, 0, dx) 

for x := 0; x < dx; x++ { 
// append can skip make statement 
pixels[y] = append(pixels[y],uint8(x*y)) 

    } 
} 

return pixels 
} 

func main() { 
    pic.Show(Pic) 
}