Conditionals Switch in

About Conditionals Switch

Like other languages, Go also provides a switch statement. Switch statements are a shorter way to write long if ... else if statements.

Basic usage

To make a switch, we start by using the keyword switch followed by a value or expression. We then declare each one of the conditions with the case keyword. We can also declare a default case, that will run when none of the previous case conditions matched:

operatingSystem := "windows"

switch operatingSystem {
case "windows":
    // do something if the operating system is windows
case "linux":
    // do something if the operating system is linux
case "macos":
    // do something if the operating system is macos
default:
    // do something if the operating system is none of the above
}

If we want to run the same piece of code for several cases, we can group them together in a single case, separating them with a ,:

operatingSystem := "windows"

switch operatingSystem {
case "windows", "linux":
    // do something if the operating system is windows or linux
case "macos":
    // do something if the operating system is macos
default:
    // do something if the operating system is none of the above
}

Cases with boolean expressions

One interesting thing about switch statements, is that the value after the switch keyword can be omitted, and we can have boolean conditions for each case. This effectively can be a shorter way to write complex if ... else statements:

age := 21

switch {
case age > 20 && age < 30:
    // do something if age is between 20 and 30
case age == 10:
    // do something if age is equal to 10
default:
    // do something else for every other case
}

Fallthrough

When the condition in a case matches, the corresponding code will run and Go will not evaluate the other case conditions by default. We can make use of the fallthrough keyword to tell Go to evaluate the other case conditions. Take this example:

age := 21

switch {
case age > 20:
    // do something if age is greater than 20
case age > 30:
    // WARNING: code here will never run. If age is greater than 30,
    // it is also greater than 20, which means only the previous case will run
default:
    // do something else for every other case
}

We can correct this code by using the fallthrough keyword:

age := 21

switch {
case age > 20:
    // do something if age is greater than 20
    fallthrough
case age > 30:
    // Since the previous case uses 'fallthrough',
    // this code will now run if age is also greater than 30
default:
    // do something else for every other case
}

To learn more about this topic, check Go by Example: Switch or Tour of Go: Switch.