How Can I Efficiently Slice Keys from a Go Map?

Slicing Keys from Maps in Go

Question:

Is there a more efficient way to obtain a slice of keys from a map in Go?

Currently, a common approach is to iterate over the map, copying the keys into a slice:

i := 0
keys := make([]int, len(mymap))
for k := range mymap {
    keys[i] = k
    i++
}

Answer:

Using the make function with the specified slice capacity can improve efficiency by eliminating the need for reallocations:

keys := make([]int, len(mymap))

i := 0
for k := range mymap {
    keys[i] = k
    i++
}

This approach is slightly more concise and eliminates the overhead associated with appending to a slice. In tests with maps containing large numbers of keys, it has been shown to be 20% faster than using the append function.

While the make function sets the capacity of the slice, it's worth noting that append still incurs some additional overhead checking if the capacity has been reached on each append. Assigning array members directly can provide a performance improvement in this case.

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