What is the difference between require() and return in an if() statement?

Question

I am reading this page and trying to understand how these 2 pieces of code will behave:

With require()

function transfer(address _newOwner) public {
    require(msg.sender == owner)
    // Do the actual transfer
}

With return in an if():

function transfer(address _newOwner) public {
    if (msg.sender != owner) return;
    // Do the actual transfer
}

I understand that require() will revert all changes and refund me any unused gas, but what exactly does the second code will behave? The function will stop executing, but does it refund unused gas?

Thanks

Answer 1

The second function returns execution to the previous function. So for example if you have something like this:

pragma solidity 0.6.0;

contract Example {

    address owner;
    event SomeEvent();
    event OtherEvent();

    function doSomething(address _someowner) public {
        transfer2(_someowner);
        emit SomeEvent();
        transfer1(_someowner);
        emit OtherEvent();
    }

    function transfer1(address _newOwner) public {
        require(msg.sender == owner);
        // Do the actual transfer
    }

    function transfer2(address _newOwner) public {
        if (msg.sender != owner) return;
        // Do the actual transfer
    }
}

So what happens if you call doSomething with:

1) _someowner equals to owner:

• transfer2 performs the transfer
• event SomeEvent is emitted
• transfer1 performs the transfer
• event OtherEvent is emitted

2) _someowner does not equal to owner:

• transfer2 does not perform the transfer but returns execution to previous function (doSomething)
• event SomeEvent is emitted
• transfer1 does not perform the transfer and halts the transaction execution with an error
• event OtherEvent is not emitted as the execution never reaches this far

Answer 2

I found this to be helpful.

The answer also has a link to the official docs.