Arrays

In Sway, an Array is a fixed-size collection of elements of the same type, similar to a Tuple. Arrays can hold arbitrary types, including non-primitive types, with their size determined at compile time.

Using Arrays in the SDK

You can pass a TypeScript Array into your contract method seamlessly just like you would pass an Array to a TypeScript function.

The SDK handles the conversion from TypeScript to Sway in the background, allowing the expected data to be passed through the type regardless of the Array type.

An Array in Sway is simply a typed Array, as demonstrated in the following example:

// in Sway: [u8; 5]
const numberArray: number[] = [1, 2, 3, 4, 5];

// in Sway: [bool; 3]
const boolArray: boolean[] = [true, false, true];

See code in context

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In Sway, Arrays are fixed in size, so the storage size is determined at the time of program compilation, not during runtime.

Let's say you have a contract that takes an Array of type u64 with a size length of 2 as a parameter and returns it:

fn echo_u64_array(u64_array: [u64; 2]) -> [u64; 2] {
    u64_array
}

See code in context

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To execute the contract call using the SDK, you would do something like this:

const u64Array: [BigNumberish, BigNumberish] = [10000000, 20000000];

const { value } = await contract.functions.echo_u64_array(u64Array).get();

console.log('value', value);
// [<BN: 0x989680>, <BN: 1312D00>]

See code in context

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You can easily access and validate the Array returned by the contract method, as demonstrated in the previous example.

As previously mentioned, Sway Arrays have a predefined type and size, so you need to be careful when passing Arrays as parameters to contract calls.

Passing an Array with an incorrect size, whether it has more or fewer elements than the specified length, will result in an error:

try {
  // @ts-expect-error forced error
  await contract.functions.echo_u64_array([10000000]).get();
} catch (e) {
  console.log('error', e);
  // Types/values length mismatch.
}

See code in context

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Similarly, passing an Array with an incorrect type will also result in an error:

try {
  await contract.functions.echo_u64_array([10000000, 'a']).get();
} catch (e) {
  console.log('error', e);
  // Invalid u64.
}

See code in context

Vectors

If your Array size is unknown until runtime, consider using the Vectors type, which is more suitable for dynamic-sized collections.