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,
    ) {
        let call_params = CallParams {
            coins: 0,
            asset_id: AssetId::from(ZERO_B256),
            gas: 10_000,

        call_with_function_selector(target, function_selector, calldata, call_params);

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

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

    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 = encode_fn_selector("set_value_multiple_complex");
        let call_data = calldata!(
            MyStruct {
                a: true,
                b: [1, 2, 3],


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