Fallback functions [solidity]

 pragma solidity ^0.5.12;

// contract with fallback function

contract fall {

  uint n;

  function set(uint value) external {

    n = value;

  }

  function() external payable {

    n = 0;

  }

}

// contract to interact with contract fall

contract Sendeth {

  function callfall(fall a) public returns (bool) {

     // calling a non-existing function

      (bool success,) = address(a).call(abi.encodeWithSignature("setter()"));

      require(success);

      // sending ether to contract fall

      address payable payableA = address(uint160(address(a)));

      return(payableA.send(2 ether));

   }

}

fallback() external payable

This is a fallback function. It is declared payable, which allows it to accept transfer value.

• It is called in the following scenarios:

• A contract receives only ether and no data

No function calls matched even though the account received data

With this statement (bool success,) = address(a).call(abi.encodeWithSignature("setter()")); we are calling a function signature in contract fall that does not exist. That’s why this call would go to the fallback function and be handled by the fallback function.