Variable outputs

In some cases, you might want to send funds to the output of a transaction. Sway has a specific method for that: transfer_to_address(coins, asset_id, recipient)`. So, if you have a contract that does something like this:

    fn transfer_coins_to_output(coins: u64, asset_id: ContractId, recipient: Address) {
        transfer_to_address(coins, asset_id, recipient);
    }

With the SDK, you can call transfer_coins_to_output by chaining append_variable_outputs(amount) to your contract call. Like this:

        let address = wallet.address();

        // withdraw some tokens to wallet
        let response = contract_methods
            .transfer_coins_to_output(1_000_000, contract_id.into(), address.into())
            .append_variable_outputs(1)
            .call()
            .await?;

append_variable_outputs effectively appends a given amount of Output::Variables to the transaction's list of outputs. This output type indicates that the output's amount and the owner may vary based on transaction execution.

Note that the Sway lib-std function mint_to_address calls transfer_to_address under the hood, so you need to call append_variable_outputs in the Rust SDK tests like you would for transfer_to_address.