Receive and Fallback

On the EVM target, the route names receive and fallback are reserved and lower to Solidity’s special functions of the same name.

Shape rules

Both routes must:

• take no parameters;
• declare no return type;
• not be marked view or pure.

An entity may declare at most one receive and at most one fallback (V41). Shape violations are V40.

receive

Handles plain native-currency transfers with empty calldata (the usual ETH receiver). Write it with the required accept keyword so the generated function is payable:

entity EthVault {
    routes {
        accept receive() => [
            // credit balance via member transforms, emit, etc.
        ]
    }

    m_deposited: U256 {
        in receive() => m_deposited + msg::value
    }
}

Treat accept receive() as the language spelling of a payable ETH receiver — empty calldata, native value welcome. The generated Solidity is receive() external payable.

fallback

Runs when a call has no matching function selector (and is not a plain ETH send that hits receive):

entity EthVault {
    routes {
        accept receive() => []

        fallback() => [
            // optional catch-all
        ]
    }
}

fallback becomes payable automatically if (and only if) the body or its transforms read msg::value.