Contains method for a slice

Is there anything similar to a slice.contains(object) method in Go without having to do a search through each element in a slice?

Solution 1:

Mostafa has already pointed out that such a method is trivial to write, and mkb gave you a hint to use the binary search from the sort package. But if you are going to do a lot of such contains checks, you might also consider using a map instead.

It's trivial to check if a specific map key exists by using the value, ok := yourmap[key] idiom. Since you aren't interested in the value, you might also create a map[string]struct{} for example. Using an empty struct{} here has the advantage that it doesn't require any additional space and Go's internal map type is optimized for that kind of values. Therefore, map[string] struct{} is a popular choice for sets in the Go world.

Solution 2:

No, such method does not exist, but is trivial to write:

func contains(s []int, e int) bool {
    for _, a := range s {
        if a == e {
            return true
        }
    }
    return false
}

You can use a map if that lookup is an important part of your code, but maps have cost too.

Solution 3:

The sort package provides the building blocks if your slice is sorted or you are willing to sort it.

input := []string{"bird", "apple", "ocean", "fork", "anchor"}
sort.Strings(input)

fmt.Println(contains(input, "apple")) // true
fmt.Println(contains(input, "grow"))  // false

...

func contains(s []string, searchterm string) bool {
    i := sort.SearchStrings(s, searchterm)
    return i < len(s) && s[i] == searchterm
}

SearchString promises to return the index to insert x if x is not present (it could be len(a)), so a check of that reveals whether the string is contained the sorted slice.

Solution 4:

If the slice is sorted, there is a binary search implemented in the sort package.