Low-level calls

With low-level calls, you can specify the parameters of your calls at runtime and make indirect calls through other contracts.

Your caller contract should call std::low_level_call::call_with_function_selector, providing:

• target contract ID
• function selector encoded as Bytes
• calldata encoded as Bytes
• whether the calldata contains only a single value argument (e.g. a u64)
• std::low_level_call::CallParams

    fn call_low_level_call(
        target: ContractId,
        function_selector: Bytes,
        calldata: Bytes,
        single_value_type_arg: bool,
    ) {
        let call_params = CallParams {
            coins: 0,
            asset_id: AssetId::from(ZERO_B256),
            gas: 10_000,
        };

        call_with_function_selector(
            target,
            function_selector,
            calldata,
            single_value_type_arg,
            call_params,
        );
    }

On the SDK side, you can construct an encoded function selector using the fuels::core::fn_selector! macro, and encoded calldata using the fuels::core::calldata! macro.

E.g. to call the following function on the target contract:

    #[storage(write)]
    fn set_value_multiple_complex(a: MyStruct, b: str[4]);

you would construct the function selector and the calldata as such, and provide them to the caller contract (like the one above):

        let function_selector =
            fn_selector!(set_value_multiple_complex(MyStruct, SizedAsciiString::<4>));
        let call_data = calldata!(
            MyStruct {
                a: true,
                b: [1, 2, 3],
            },
            SizedAsciiString::<4>::try_from("fuel")?
        )?;

        caller_contract_instance
            .methods()
            .call_low_level_call(
                target_contract_instance.id(),
                Bytes(function_selector),
                Bytes(call_data),
                false,
            )
            .estimate_tx_dependencies(None)
            .await?
            .call()
            .await?;

Note: the calldata! macro uses the default EncoderConfig configuration under the hood.