Does Go Map Iteration Order Depend on Key Insertion Order?

Assignment Order in Go Maps

Considering the following Go code:

package main

import "fmt"

type Vertex struct {
    Lat, Long float64
}

var m map[string]Vertex

func main() {
    m = make(map[string]Vertex)
    m["Bell Labs"] = Vertex{
        40.68433, 74.39967,
    }
    m["test"] = Vertex{
        12.0, 100,
    }
    fmt.Println(m["Bell Labs"])
    fmt.Println(m)
}

It outputs:

{40.68433 74.39967}

map[Bell Labs:{40.68433 74.39967} test:{12 100}]

Modifying the test vertex declaration by moving the right "}" 4 spaces, as follows:

m["test"] = Vertex{
    12.0, 100,
}

Changes the output to:

{40.68433 74.39967}

map[test:{12 100} Bell Labs:{40.68433 74.39967}]

Explanation:

Map "order" in Go depends on the randomized hash function used to prevent denial of service attacks. As per the Go issue tracker (http://code.google.com/p/go/issues/detail?id=2630), map order is not guaranteed according to the specification.

According to the specification, a map is an unordered group of elements with unique keys. A future implementation could change the order of a map without modifying it in your code. Therefore, relying on specific map order is not a recommended practice in Go.

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