What does mean expression "variableName;" in Solidity?

Question

I can not find any information about this expression in docs. There is the following code on Ehternaut Re-entrancy task .

function withdraw(uint _amount) public {
  if(balances[msg.sender] >= _amount) {
    (bool result,) = msg.sender.call{value:_amount}("");
    if(result) {
      _amount;
    }
    balances[msg.sender] -= _amount;
  }
}

What does _amount; mean?

Answer 1

if(result) {
  _amount;
}

This snippet effectively does nothing. You can safely ignore it, as it's not related to the reentrancy vulnerability.

Without the mentioned snippet, the compiler would raise a warning about unused result variable. If they didn't declare the result variable, there would be another warning about not checking the result of the low-level call. And if they just left the condition block empty - yes, another warning about empty block.

So my best guess is that the authors just wanted to clear the warnings, and chose this way to do that.