why the length of this go slice is 4 and why the output has the space in slice?

I am new to golang and while running this code snippet I am getting the len as 4, trying to understand why so ?

package main

import "fmt"

type phone struct {
	model  string
	camera Camera
	ram    int
}

type Camera struct {
	lens      string
	aparature int
}

func main() {

	var m = make(map[string]phone)

	myphn1 := phone{model: "iphone", camera: Camera{"20", 4}, ram: 6}
	myphn2 := phone{model: "pixel", camera: Camera{"50", 2}, ram: 6}

	m["myphn1"] = myphn1
	m["myphn2"] = myphn2

	var k = make([]string, len(m))

	for key, _ := range m {
		k = append(k, key)
	}

	fmt.Println(k)
	fmt.Println(len(k))

}

I understand this adds size of 2 while creating, but while printing it gives somelike this , is the space in answer for 2 unallocated entries ?

[  myphn2 myphn1]
4

This creates a slice of length 2 (len(m) is 2 here):

var k = make([]string, len(m))

This adds two elements to it, for a total of 4:

for key, _ := range m {
    k = append(k, key)
}

If you want to preallocate a slice, you need to provide a length of zero along with the desired capacity:

var k = make([]string, 0, len(m))

This is covered with examples in the Tour of Go.

You create a slice with length 2, and appended two more elements to it, so the length is 4.

what you probably want to do is to create a slice with capacity 2:

var k = make([]string,0,len(m))