英文:
Go language: Type XXX is not an expression
问题
我写了一个函数：
func Pic(dx, dy int) [][]uint8 {
type matrix [][]uint8
for i := 0; i < dx; i++ { // 用 z 的正确位置填充矩阵。
for j := 0; j < dy; j++ {
matrix[i][j] = Z(i,j)
}
}
return matrix
}
这个函数的目的是为每个 x 和 y 值填充一个包含 z 值的矩阵，并返回它。由于我想根据 Pic 函数的参数设置矩阵的不同维度，所以我在第 2 行创建了一个切片。然后在我的循环中填充矩阵。
运行这段代码时，我收到一个错误：type matrix is not an expression，出现在 matrix[i][j] = Z(i,j) 这一行。我做错了什么？matrix[i][j] 应该评估为一个表达式吗？为什么应该这样，当我想要在那里放置一些东西时（它现在是空的/不存在！）？
英文:
I have written a function:
func Pic(dx, dy int) [][]uint8 {
type matrix [][]uint8
for i := 0; i < dx; i++ { // fills up the matrix with z's in their right places.
for j := 0; j < dy; j++ {
matrix[i][j] = Z(i,j)
}
}
return matrix
}
that is supposed to fill up a matrix with z values for each x and y value and return it. As I want to have different dimensions for the matrix depending of parameters to the Pic function, I create a slice i line 2. Then in my for loops i fill the matrix up.
I get an error upon running this code: type matrix is not an expression for the matrix[i][j] = Z(i,j) line. What am I doing wrong? Should matrix[i][j] evaluate to an expression? Why should it, when I want to put something there (it's empty/non-existent now!) ?
答案1
得分: 6
你将matrix声明为一种类型，但在使用时将其作为变量。
尝试使用以下代码：
var matrix [][]uint8
英文:
You're declaring matrix as a type, but using it as a variable.
try:
var matrix [][]uint8
答案2
得分: 4
你可以使用var matrix [][]uint8，但我建议使用内置的make函数，因为你知道外部切片的长度dx和内部切片的长度dy。Effective Go的Two-dimensional slices部分提供了使用make函数分配二维切片的示例。下面是一个适用于你的Pic函数的示例代码：
func Pic(dx, dy int) [][]uint8 {
matrix := make([][]uint8, dx)
for i := 0; i < dx; i++ {
matrix[i] = make([]uint8, dy)
for j := 0; j < dy; j++ {
matrix[i][j] = Z(i, j)
}
}
return matrix
}
英文:
While you can use var matrix [][]uint8, I'd recommend using the built-in make function since you know the desired lengths—dx for the outer slice and dy for the inner slice. The Two-dimensional slices section of Effective Go gives an example of using make to allocate a two-dimensional slice. Below is an example for your Pic function.
func Pic(dx, dy int) [][]uint8 {
matrix := make([][]uint8, dx)
for i := 0; i < dx; i++ {
matrix[i] = make([]uint8, dy)
for j := 0; j < dy; j++ {
matrix[i][j] = Z(i, j)
}
}
return matrix
}
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