How to pass multidimensional array in arbitrary size as function argument in GO

Question

I'm new to GO. There is the problem I'm facing.

The function takes a 2D array in arbitrary size as argument:

func PrintArray(a [][]string) {
    for _, v1 := range a {
        for _, v2 := range v1 {
            fmt.Printf("%s ", v2)
        }
        fmt.Printf("\n")
    }
}

As you can see, since the nested loop uses range. The size of the array really doesn't matter.

But when I try to call this function:

a := [3][2]string{
    {"line", "tiger"},
    {"cat", "dog"},
    {"pigeon", "hamster"},
}
PrintArray(a[:])

It complains about:

cannot use a[:] (type [][2]string) as type [][]string in argument to PrintArray

However, it won't compile with a[:][:] either.

What is the correct way to define a multidimensional array in arbitrary size in GO lang?

peterSO · Accepted Answer · 2019-03-20 22:41:34Z

4

In Go, array types and slice types are distinct. Pass slices to slices.

For example,

package main

import (
    "fmt"
)

func main() {
    a := [][]string{
        {"line", "tiger"},
        {"cat", "dog"},
        {"pigeon", "hamster"},
    }
    PrintSlices(a)
}

func PrintSlices(a [][]string) {
    for _, v1 := range a {
        for _, v2 := range v1 {
            fmt.Printf("%s ", v2)
        }
        fmt.Printf("\n")
    }
}

Playground: https://play.golang.org/p/3mPDTIEUQmT

Output:

line tiger 
cat dog 
pigeon hamster

To allocate a matrix:

package main

import (
    "fmt"
)

func NewMatrix(rows, cols int) [][]int {
    m := make([][]int, rows)
    for r := range m {
        m[r] = make([]int, cols)
    }
    return m
}

func main() {
    m := NewMatrix(3, 2)
    fmt.Println(m)
}

Playground: https://play.golang.org/p/qvwQu2giRcP

Output:

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

edited Mar 20, 2019 at 22:41

answered Mar 20, 2019 at 22:20

peterSO

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2 Comments

FisNaN Over a year ago

Is there a way to define the size of inner array?

peterSO Over a year ago

See my revised answer.

andrel · Accepted Answer · 2019-03-20 22:41:49Z

1

Interesting question. This should work

a := [][]string{
    {"line", "tiger"},
    {"cat", "dog"},
    {"pigeon", "hamster"},
}
PrintArray(a[:])

From the error messages, I would guess that arrays defined with size are of different types.

For example, if the PrintArray looks like this:

func PrintArray(a [3][2]string) {

Then you can pass it an array defined as:

a := [3][2]string.

If we vary the numbers in either the PrintArray method or a, so that they differ, we get an error message that says:

cannot use a (type [3][2]string) as type [3][1]string in argument to PrintArray

edited Mar 20, 2019 at 22:41

answered Mar 20, 2019 at 22:17

andrel

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