Store a reference to a value type?

Question

I am writing a \"Monitor\" object to facilitate debugging of my app. This Monitor object can be accessed at run time from an IronPython interpreter. My question is, is it po

Answer 1

Here is a pattern I came up with that I find myself using quite a bit. Usually in the case of passing properties as parameters for use on any object of the parent type, but it works just as well for a single instance. (doesn't work for local scope value types tho)

public interface IValuePointer
{
    T Value { get; set; }
}
public class ValuePointer : IValuePointer
{
    private readonly TParent _instance;
    private readonly Func _propertyExpression;
    private readonly PropertyInfo _propInfo;
    private readonly FieldInfo _fieldInfo;

    public ValuePointer(TParent instance, 
                        Expression> propertyExpression)
    {
        _instance = instance;
        _propertyExpression = propertyExpression.Compile();
        _propInfo = ((MemberExpression)(propertyExpression).Body).Member as PropertyInfo;
        _fieldInfo = ((MemberExpression)(propertyExpression).Body).Member as FieldInfo;
    }

    public TType Value
    {
        get { return _propertyExpression.Invoke(_instance); }
        set
        {
            if (_fieldInfo != null)
            {
                _fieldInfo.SetValue(_instance, value);
                return;
            }
            _propInfo.SetValue(_instance, value, null);
        }
    }
}

This can then be used like so

class Test
{
    public int a;
}
void Main()
{
    Test testInstance = new Test();
    var pointer = new ValuePointer(testInstance,x=> x.a);
    testInstance.a = 5;
    int copyOfValue = pointer.Value;
    pointer.Value = 6;
}

Notice the interface with a more limited set of template arguments, this allows you to pass the pointer to something that has no knowledge of the parent type.

You could even implement another interface with no template arguments that calls .ToString on any value type (don't forget the null check first)