在golang中包含整数和nil值的数组？

Question

I am new to golang. But I couldn't find an answer to this.

In python I can do,

array = [1, 2, 3, None, 5]

But in go when I write

var array = [5]int {1, 2, 3, nil, 5}

The compiler gives me the following error:

cannot convert nil to type int

How can I create an array in golang which is a mix of integer and nil values?

Answer 1

First a bit of theory. Python is a dynamically typed language. While each individual value has a type, your variables can be assigned values of any type without a problem. As a consequence, python collections can contain multiple types of values and don't complain. The following is a valid python tuple (1, 'a', None, True). Go is a statically typed language. If your variable is defined as an integer you cannot assign any non-integer value to it. As a consequence, collections in Go have a type and can only contain a single type of object.

Now to practice. There are a few ways to do what you want. The classical C way would be to pick an integer value you are never going to encounter and use that as a null value. A 0 or a -1 or something. This is not very robust though.

A more idiomatic way is to define your own type.

package main

import "fmt"

type NilInt struct {
    value int
    null  bool
}

func (n *NilInt) Value() interface{} {
    if n.null {
        return nil
    }
    return n.value
}

func NewInt(x int) NilInt {
    return NilInt{x, false}
}

func NewNil() NilInt {
    return NilInt{0, true}
}

func main() {
    var x = []NilInt{NewNil(), NewInt(10), NewNil(), NewInt(5)}
    for _, i := range x {
        fmt.Printf("%v ", i.Value())
    }
}