Icon LinkOptions

Sway provides the Option (optional) container for handling variables that can have a value or be marked as no-value. This concept is useful when dealing with situations where a variable may or may not have a defined value.

In this guide, we'll explain how to work with Option types in Sway and demonstrate their usage through a practical example.

Icon LinkOverview of Option Type

The Option type in Sway is a special wrapper type of Enum. In TypeScript, you can represent the Option type by using the undefined keyword, as shown in the following example

// Sway Option<u8>
const input1: number | undefined = 10;

In this example, the variable input1 can be either a number or undefined.

Icon LinkExample: Option<u8> Parameters

Let's say we have a contract function that accepts two Option<u8> parameters. Both of these parameters can have a value or be undefined. The function checks whether each input has a value; if not, it assigns a value of 0. Finally, the function returns the sum of the two inputs.

Here's the contract function written in Sway:

fn sum_optional_u8(input1: Option<u8>, input2: Option<u8>) -> u8 {
	let value1 = match input1 {
	Option::Some(v) => v,
	Option::None => 0,
	};
 
	let value2 = match input2 {
	Option::Some(v) => v,
	Option::None => 0,
	};
 
	value1 + value2
}

You can interact with the contract function using the SDK as follows:

const input1: number | undefined = 10;
 
const input2: number | undefined = 5;
 
const { value } = await contract.functions
	.sum_optional_u8(input1, input2)
	.txParams({ gasLimit: 10_000 })
	.simulate();
 
expect(value).toEqual(input1 + input2);

In this case, the result of the contract function call is the sum of both input parameters. If we pass only one parameter, the contract function will default the other parameter's value to 0.

const input: number | undefined = 5;
 
const { value } = await contract.functions
	.sum_optional_u8(input)
	.txParams({ gasLimit: 10_000 })
	.simulate();
 
expect(value).toEqual(input);

Using Option types in Sway allows you to elegantly handle situations where a variable may or may not have a defined value.