This topic is about Solidity – Fallback Function.
Fallback function is a special function available to a contract. It has following features −
- It is called when a non-existent function is called on the contract.
- It is required to be marked external.
- It has no name.
- It has no arguments
- It can not return any thing.
- It can be defined one per contract.
- If not marked payable, it will throw exception if contract receives plain ether without data.
Following example shows the concept of a fallback function per contract.
Example
pragma solidity ^0.5.0;
contract Test {
uint public x ;
function() external { x = 1; }
}
contract Sink {
function() external payable { }
}
contract Caller {
function callTest(Test test) public returns (bool) {
(bool success,) = address(test).call(abi.encodeWithSignature("nonExistingFunction()"));
require(success);
// test.x is now 1
address payable testPayable = address(uint160(address(test)));
// Sending ether to Test contract,
// the transfer will fail, i.e. this returns false here.
return (testPayable.send(2 ether));
}
function callSink(Sink sink) public returns (bool) {
address payable sinkPayable = address(sink);
return (sinkPayable.send(2 ether));
}
}
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