GoLang：返回任意类型的2d切片

Question

I know how to create a 2D slice like this.

var data []int
data = make([]int, w*h)
v := make([][]int, h)
for i := 0; i < h; i++ {
    v[i] = data[w*i : w*(i+1)]
}

Since this is very verbose and I'm going to create many of these, I decided to refactor it into a function.

func create2dSlice(w, h int) [][]int {
    var data []int
    data = make([]int, w*h)
    v := make([][]int, h)
    for i := 0; i < h; i++ {
        v[i] = data[w*i : w*(i+1)]
    }
    return v
}

func main() {
    a := create2dSlice(3, 2)
}

This works only for integers. It there any way in golang to do this for other types reusing the same code?

I come from C++ and I would expect to be able to do something like this.

create2dSlice<int>(w, h)

Answer 1

Go doesn't have generics. For matrices, a similar problem, I have a NewMatrix function in a matrix.go file in my snippet folder. By design, I can simply copy it and do a global change of []int to another type, for example, []float64.

You could improve your function by giving w slices a valid capacity.

For example,

package main

import "fmt"

func NewMatrix(r, c int) [][]int {
    a := make([]int, c*r)
    m := make([][]int, r)
    lo, hi := 0, c
    for i := range m {
        m[i] = a[lo:hi:hi]
        lo, hi = hi, hi+c
    }
    return m
}

func create2dSlice(w, h int) [][]int {
    a := make([]int, w*h)
    s := make([][]int, h)
    lo, hi := 0, w
    for i := range s {
        s[i] = a[lo:hi:hi]
        lo, hi = hi, hi+w
    }
    return s
}

func main() {
    r, c := 2, 3
    m := NewMatrix(r, c)
    fmt.Println(m)
    w, h := c, r
    a := create2dSlice(w, h)
    fmt.Println(a)
}

Output:

[[0 0 0] [0 0 0]]
[[0 0 0] [0 0 0]]

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The Go Programming Language Specification

Slice expressions

Slice expressions construct a substring or slice from a string, array, pointer to array, or slice. There are two variants: a simple form that specifies a low and high bound, and a full form that also specifies a bound on the capacity.

Full slice expressions

For an array, pointer to array, or slice a (but not a string), the primary expression

a[low : high : max]

constructs a slice of the same type, and with the same length and elements as the simple slice expression a[low : high]. Additionally, it controls the resulting slice's capacity by setting it to max - low.