How Can I Efficiently Map an Array of Objects in Go?

Mapping an Array of Objects in Go

In Node.js, you can use the map function to transform an array of objects into an array of values. Wondering how to achieve this in Go with conciseness?

Go Solution: Map as a Top-Level Function

Unlike methods in Go, top-level functions can take additional type arguments. Using this, we can define Map as a generic function:

func Map[T, U any](ts []T, f func(T) U) []U {
    us := make([]U, len(ts))
    for i := range ts {
        us[i] = f(ts[i])
    }
    return us
}

Now, you can use this function as follows:

names := []string{"Alice", "Bob", "Carol"}
fmt.Println(Map(names, utf8.RuneCountInString)) // Output: [5 3 5]

Historical Context: Why Map is Absent in Standard Go Libraries

Prior to Go 1.18, extensive discussions in the GitHub issue for the golang.org/x/exp/slices proposal considered adding a Map function but ultimately decided against it due to concerns about:

• Hidden costs of operations within one-liners
• Uncertain error handling within Map
• Encouraging a style that deviates from Go's traditional approach

Streams API is considered a potential future home for such a function.

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