What's so bad about ref parameters?

Question

I'm faced with a situation that I think can only be solved by using a ref parameter. However, this will mean changing a method to always accept a ref parameter when I only need the functionality provided by a ref parameter 5% of the time.

This makes me think "whoa, crazy, must find another way". Am I being stupid? What sort of problems can be caused by a ref parameter?

Edit

Further details were requested, I don't think they are entirely relevant to what I was asking but here we go.

I'm wanting to either save a new instance (which will update with the ID which may later be used) or retrieve an existing instance that matches some logic and update that, save it then change the reference of the new instance to point to the existing one.

Code may make it clearer:

protected override void BeforeSave(Log entity)
{
    var newLog = entity;

    var existingLog = (from log in repository.All()
                           where log.Stuff == newLog.Stuff 
                                 && log.Id != newLog.Id
                           select log).SingleOrDefault();

    if (existingLog != null)
    {
        // update the time
        existingLog.SomeValue = entity.SomeValue;
        // remove the reference to the new entity
        entity = existingLog;
    }
}

// called from base class which usually does nothing before save
public void Save(TEntity entity)
{
    var report = validator.Validate(entity);

    if (report.ValidationPassed)
    {
        BeforeSave(entity);
        repository.Save(entity);
    }
    else
    {
        throw new ValidationException { Report = report };
    }
}

It's the fact that I would be adding it in only for one child (so far) of the base class that prevents me using an overload (due to the fact I would have to duplicate the Save method). I also have the problem whereby I need to force them to use the ref version in this instance otherwise things won't work as expected.

Answer 1

Can you add an overload? Have one signature without the ref parameter, and one with it.

Ref parameters can be useful, and I'm glad they exist in C#, but they shouldn't be used without thought. Often if a method is effectively returning two values, it would be better either to split the method into two parts, or encapsulate both values in a single type. Neither of these covers every case though - there are definitely times when ref is the best option.