Test if a map incorporates a key in Go (Golang)

To verify if a given key exists in a map in Go, use the particular type of the index expression

v, okay := a[k]

which returns two components – a price v of the map with the important thing ok, and a boolean worth okay equal to true if the important thing ok is current within the map. If not, the okay is fake.

Instance

information := map[string]int{
    "a": 1,
    "b": 2,
    "c": 3,
}

val, okay := information["a"]
fmt.Println(val, okay)
val, okay = information["d"]
fmt.Println(val, okay)

Output:

Methods to verify if a key exists in a map straight in an if assertion

In on a regular basis coding, a standard state of affairs is that you just solely need to execute a sure piece of code if a given key exists within the map. In Go, you are able to do this by combining the if assertion with the map index expression.

if val, okay := information["a"]; okay {
    fmt.Println(val, okay)
}
if val, okay := information["d"]; okay {
    fmt.Println(val, okay)
}

Output:

If statements will be preceded by easy statements that will let you assign map values straight within the if, earlier than evaluating it.

Why is checking for zero values not adequate?

Chances are you’ll be questioning why we can’t use the easier map index expression which returns a single worth and verify if it’s not the zero worth:

if information["a"] != 0 {
    fmt.Println("key a exists")
}

Output:

It really works wonderful in case you are certain that your map doesn’t include zero values. In any other case, the end result will likely be incorrect:

// incorrect end result
information["d"] = 0
if information["d"] != 0 {
    fmt.Println("key d exists")
} else {
    fmt.Println("key d doesn't exist")
}

Output:

Because of this, it’s a higher concept to make use of a two-values map index expression for checking whether or not a map incorporates a given key in Go.