Question

I’m having some problems with encapsulation in C#. There are two specific scenarios that are causing me problems and I believe the issue is related.

Scenario #1

I have a class definition that looks something like this

class MyClass
{
  private int _someField;
  private OtherClass _otherClass;

  public int someField
  {
    get { return _someField; }
    set { _someField = value; }
  }

  public OtherClass otherClass
  {
    get { return _otherClass; }
    set { _otherClass = value; }
  }

}

If I then try and do something like this in a new piece of code

MyClass theClass = new MyClass();

theClass.otherClass.XYZ += 1;

I get told Cannot Modify the return value of ‘MyClass.otherClass’ because it is not a variable.

Scenario 2#

public partial class trksegType
{

    private wptType[] trkptField;

    private extensionsType extensionsField;

    /// <remarks/>
    [System.Xml.Serialization.XmlElementAttribute("trkpt")]
    public wptType[] trkpt
    {
        get
        {
            return this.trkptField;
        }
        set
        {
            this.trkptField = value;
        }
    }
}

If I now try and foreach through the wptType array:

foreach (wptType way in trk.trkseg[i])

I get told – foreach statement cannot operate on variables of type ‘trksegType’ because ‘trksegType’ does not contain a public definition for ‘GetEnumerator’

Even though an array should implicitly allow enumeration.

Can anyone explain what’s going on and what I can do to get around this problem, whilst still maintaining best practices.

Answer 1

(You really shouldn’t post two questions in one.)

Scenario 1

Cannot Modify the return value of ‘MyClass.otherClass’ because it is not a variable.

This error happens because OtherClass is not a class, but a struct — also called a value type. This means that accessing MyClass.otherClass copies the value instead of returning a reference. You would be modifying this copy, which would be pointless. The compiler catches this because it is always a bug and never useful.

Scenario 2

foreach (wptType way in trk.trkseg[i])

You haven’t told us what trkseg[i] is, but if it is of the type trksegType, then the answer is: because trksegType doesn’t allow any enumeration. It does not implement IEnumerable, IEnumerable<T>, nor does it have a GetEnumerator method of its own.

Perhaps you meant to write:

foreach (wptType way in trk.trkseg[i].trkpt)

because trkpt is an array of wptType. (You might have found this error sooner if you used more meaningful variable names instead of weird combinations of letters that make no sense.)