Switch Blocks

Switch blocks consists of the following new keywords:

• case
• switch
• default

Switch Statement

pluto
local value = 1
switch value do
    case 1:
        print("There is only one!")
        break
    case 2:
        print("There is only two!")
        break
end
-- Break jumps here.

Switch statements also support fallthrough.

pluto
local value = 1
switch value do
    case 1:
    case 2:
    case 3:
    case 4:
    case 5:
        print("Got 1-5.")
        break
    default:
        print("Value is greater than 5.")
end
-- Break jumps here.

In this example, cases 1-4 fall through to case 5.

Remember to use break whenever you do not want fallthrough. Here is an example of a potential bug:

pluto
local value = 1
switch value do
    case 1:
        print("There is only one!")
    case 2:
        print("There is only two!")
end
-- Output:
--  There is only one!
--  There is only two! <-- Uh oh.

The default case is executed if none of the other cases are true. For example:

pluto
local value = 1
switch value do
    case 2:
    case 3:
        break
    default:
        print("Value is neither 2 nor 3!")
end

The default case can be placed anywhere in the block. It also supports fallthrough, so remember to use break if you place it above any cases.

Case Blocks

Any expression can be used for the case condition:

pluto
switch true do
    case 42 == 42:
        print("42 is 42 is true")
        break
end

There is a short-hand fallthrough syntax:

pluto
switch value do
    case 1, 2, 3:
        print("1-3")
        break
    case 4, 5, 6:
        print("4-6")
        break
end

However, note that method calls needs to be encapsulated with parentheses:

pluto
local t = {
    function getVal()
        return 42
    end
}
switch 42 do
    case t:getVal(): -- This is interpreted as `case t: getVal():print("val is 42")`
        print("val is 42")
        break
    case (t:getVal()): -- This works as expected
        print("val is 42")
        break
end

Switch Expression

Just like ternary expressions, these allow you to conditionally provide values, with massively simplified case blocks:

pluto
local place = 1
place = switch place do
    case 1 -> "1st"
    case 2 -> "2nd"
    case 3 -> "3rd"
    default -> $"{place}th"
end
print(place) --> 1st

Note that the case blocks here have their conditions delimited by an arrow (->) instead of a colon (:).

Despite not being able to manually fall through, the shorthand fallthrough syntax still works:

pluto
local function print_range(value)
    print(switch value do
        case 1, 2, 3 -> "1-3"
        case 4, 5, 6 -> "4-6"
    end)
end
print_range(1) --> 1-3
print_range(6) --> 4-6
print_range(9) --> nil

Notice how the default case was omitted in this example, so it was implicitly set to default -> nil.

Using Compatibility Mode?

You may need to use pluto_switch instead of switch. Alternatively, pluto_use switch will enable the keyword independently of environment settings.