OO Design - do you use public properties or private fields internally? [duplicate]

Question

I'm working in C# 2.0, but this would apply to most object oriented languages. When I create classes with public properties that wrap private fields, I switch back & forth between whether I should use the property or field internally. Of course C# 3.0 makes this easier with auto-properties, but it could still apply.

Does it matter?

public class Person
{
    private string _name = "";

    public string Name
    {
        get { return _name; }
        set { _name = value; }
    }

    public Person(string name)
    {
        _name = name; //should I use the property or field here?
    }
}

Answer 1

Basically, because you can implement your validation and other logic in the property, you should access through the property unless you have a specific reason not to.

It helps with consistency within your object, because that way you know that the values of your private fields have gone through whatever rigors you choose to put in your accessor or setter methods.

On the other hand, the constructor can possibly be an exception to this, because you might want to set initial values.

But in general, I'd say access through the property.

EDIT

A (trivial/contrived) example

public class Person
{
    private string _name = "";
    private List<String> oldnames = new ArrayList();

    public string Name
    {
        get { return _name; }
        set 
        {
           oldnames.Add(_name);
           _name = value; 
        }
    }

    public Person(string name)
    {
        _name = name; //should I use the property or field here?
    }
}

So in this case, you would want the constructor to skip the property but if you EVER use the field again you'll be causing a bug in your code because you're skipping the 'name archiving'. The reason to put validation in your property is so that you don't need to duplicate the validation code in every place that you access the field, so you shouldn't skip it even in private methods.