Solidity Errors & Exceptions

Core Mechanism

When error occurs the transaction is reverted and all state changes are undone.

three main ways

1. require(): Validate external input and preconditions. when error occurs it will refund Gas. require(msg.sender == owner, "You are not the owner.");
2. assert(): It should only be used for internal errors and invariants. assert(balance == 50);
3. revert(): It is used for errors of complex logic and also refund Gas when error occurs.

contract ErrorHandling {

   error NotOwner();

   if (msg.sender != owner) {
     revert NotOwner();  //Custom Errors
   }
}

Custom Errors

Custom errors save gas compared to string error messages.