The Receive Fallback Function

Solidity 0.6/0.8 Update

Prior Solidity 0.6 the fallback function was simply an anonymous function that looked like this:


function () external {
 
}

It’s now two different functions. receive() to receive money and fallback() to just interact with the Smart Contract without receiving Ether. This example uses the updated version.

Let’s add a receive fallback function to the Smart Contract so we can simply send 1 Ether to the Contract without directly interacting with a concrete function.


//SPDX-License-Identifier: MIT
 
pragma solidity 0.8.3;
 
contract FunctionsExample {
    
    mapping(address => uint) public balanceReceived;
   
    function receiveMoney() public payable {
        assert(balanceReceived[msg.sender] + msg.value >= balanceReceived[msg.sender]);
        balanceReceived[msg.sender] += msg.value;
    }
    
    function withdrawMoney(address payable _to, uint _amount) public {
        require(_amount <= balanceReceived[msg.sender], "not enough funds.");
        assert(balanceReceived[msg.sender] >= balanceReceived[msg.sender] - _amount);
        balanceReceived[msg.sender] -= _amount;
        _to.transfer(_amount);
    } 
    
    receive() external payable {
        receiveMoney();
    }
}

Let’s try this again:

Deploy a new Version
Enter 1 Ether in the value field
Hit the Transact button
Observe the Transaction Log, see that the transaction goes through now.

ethereum-blockchain-developer-image

Did you see it? Just works like this. It even says .(receive) in the transaction. That’s great!

Now onto the constructor!