How Can I Efficiently Check List Membership in Go?

Checking List Membership in Go: An Alternative to the Python "in" Keyword

In Python, the "in" keyword provides a convenient way to check if a value exists within a list. Go, however, does not offer a direct equivalent.

Approximating the "in" Keyword with a Map

One approach in Go is to leverage a map[string]bool as a representation of a set. By storing valid values as keys and assigning true values, you can test for membership by checking if a key is present in the map:

valid := map[string]bool{"red": true, "green": true, "yellow": true, "blue": true}

if valid[x] {
    fmt.Println("found")
} else {
    fmt.Println("not found")
}

Utilizing Zero Values

Take advantage of the fact that when a key is not found in a map, the zero value for bool (false) is returned. This allows you to omit the explicit assignment of true values, simplifying the initialization:

valid := map[string]bool{"red", "green", "yellow", "blue"}

if valid[x] {
    fmt.Println("found")
} else {
    fmt.Println("not found")
}

Optimizations

For scenarios with a large number of valid values, consider using a for range loop to initialize the map. This provides a compact solution:

for _, v := range []string{"red", "green", "yellow", "blue"} {
    valid[v] = true
}

Additionally, you can optimize the code by defining a const variable to avoid repetitive boolean values:

const t = true
valid := map[string]bool{"red": t, "green": t, "yellow": t, "blue": t}

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