Options

Option types allow you to indicate that a variable or parameter can either be nil or a specified type. This is useful for representing values that may or may not be present.

Declaring Option Types

To declare an option type, prefix the type with ?. For example, a variable that can be either a string or nil:

let s: ?string = nil;

Option types cannot be nested (e.g., ??string is not allowed), as they are designed to transform into simple Lua code.

Using Options with Functions

You can use option types in function parameters:

func print_name(name: ?string) {
    if name {
        print(name?); // Use '?' to unwrap the value
    }
}

Note: The ? operator is used to unwrap the option. The compiler currently requires this even if you’ve checked that the value exists. If you try to unwrap a nil value, it will cause an error.

The else Postfix

For convenience, you can use the else postfix to provide a default value if the option is nil:

func print_name(name: ?string) {
    print(name else "no name was supplied!");
}

This will print the value of name if it exists, or "no name was supplied!" if it is nil.

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Options make it easy to handle values that may be missing, while keeping your code clear and concise.