How Can I Efficiently Check for Value Membership in Go Lists?

Checking Value Membership in Lists in Go

In Python, the in keyword conveniently checks if a value exists within a list. Similar functionality in Go requires a slightly different approach.

One option is to utilize a map with string keys and integer values. However, this approach requires specifying an unused integer value, which can be inconvenient.

Using a Map with Boolean Values

A more elegant solution involves creating a map with string keys and boolean values. The absence of a key in the map returns the default boolean value of false.

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

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

Optimizing with a Slice

If you have a large number of valid values, consider using a slice to initialize the map values to true:

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

Shorter Initialization Using Constants

Alternatively, you can create an untyped or boolean constant and optimize the initialization further:

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

By adopting one of these techniques, you can efficiently check if a value is contained within a list in Go, providing similar functionality to Python's in keyword.

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