Are booleans as method arguments unacceptable? [closed]

A colleague of mine states that booleans as method arguments are not acceptable. They shall be replaced by enumerations. At first I did not see any benefit, but he gave me an example.

What's easier to understand?

file.writeData( data, true );

Or

enum WriteMode {
  Append,
  Overwrite
};

file.writeData( data, Append );

Now I got it! ;-)
This is definitely an example where an enumeration as second parameter makes the code much more readable.

So, what's your opinion on this topic?

Boolean's represent "yes/no" choices. If you want to represent a "yes/no", then use a boolean, it should be self-explanatory.

But if it's a choice between two options, neither of which is clearly yes or no, then an enum can sometimes be more readable.

Enums also allow for future modifications, where you now want a third choice (or more).

Use the one that best models your problem. In the example you give, the enum is a better choice. However, there would be other times when a boolean is better. Which makes more sense to you:

lock.setIsLocked(True);

or

enum LockState { Locked, Unlocked };
lock.setLockState(Locked);

In this case, I might choose the boolean option since I think it's quite clear and unambiguous, and I'm pretty sure my lock is not going to have more than two states. Still, the second choice is valid, but unnecessarily complicated, IMHO.

To me, neither using boolean nor enumeration is a good approach. Robert C. Martin captures this very clearly in his Clean Code Tip #12: Eliminate Boolean Arguments:

Boolean arguments loudly declare that the function does more than one thing. They are confusing and should be eliminated.

If a method does more than one thing, you should rather write two different methods, for example in your case: file.append(data) and file.overwrite(data).

Using an enumeration doesn't make things clearer. It doesn't change anything, it's still a flag argument.