Closed Issue: IValueProvider.Value is incorrect unless IValueProvider is being observed !? [5674]

Hi Thomas

I've just started using Obtics and on the whole it's excellent. Well done!

I understand there are a few undocumented gotchas (eg. http://obtics.codeplex.com/Thread/View.aspx?ThreadId=68881), but I believe I've found a nasty bug whereby the IValueProvider<>.Value is incorrect when;
a. Expression contains System.Linq.Enumerable.Intersect() that returns non-zero AND
b. IValueProvider isn't bound/observed.

The following code illustrates the problem;
a. Class A - expression without Intersect that works without requiring the obtics property to be observed.
b. Class B - expression with Intersect that fails unless the obitcs property is observed.

I'm assuming the problem isn't unique to Intersect(), but instead possibly related to;
- inter-dependencies in the constructed expression tree?
- delayed execution not firing when the IValueProvider<>.Value is read? I suspect this is the issue.

I'd *really* appreciate a fix to this issue as these expressions are typical (albeit it more complex) of those I need to observe.

Many Thanks


using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Linq;
using Obtics.Values;

namespace ObticsValueTest
{
// simpler expression that doesn't involve Intersect()
public class A
{
public ObservableCollection<object> OC1 = new ObservableCollection<object>();
public ObservableCollection<object> OC2 = new ObservableCollection<object>();

public int Method()
{
return OC1.Count() + OC2.Count();
}
public IValueProvider<int> Property
{
get { return ExpressionObserver.Execute(() => OC1.Count() + OC2.Count()); }
}
}

// more cmplex expression using Intersect()
public class B
{
public ObservableCollection<object> OC1 = new ObservableCollection<object>();
public ObservableCollection<object> OC2 = new ObservableCollection<object>();

public int Method()
{
return OC1.Intersect(OC2).Count();
}
public IValueProvider<int> Property
{
get { return ExpressionObserver.Execute(() => OC1.Intersect(OC2).Count()); }
}
}


class Program
{
static void Main()
{
// works
var a1 = new A();
Test(a1);

// works
var b1 = new B();
((INotifyPropertyChanged) b1.Property).PropertyChanged += (s, e) => { };
Test(b1);

// fails
var b2 = new B();
Test(b2);
}

static void Test(A a)
{
var o1 = new object();
var o2 = new object();

a.OC1.Add(o1);
if (a.Method() != a.Property.Value)
throw new Exception();

a.OC2.Add(o1);
if (a.Method() != a.Property.Value)
throw new Exception();

a.OC2.Add(o2);
if (a.Method() != a.Property.Value)
throw new Exception();
}

static void Test(B b)
{
var o1 = new object();
var o2 = new object();

b.OC1.Add(o1);
if (b.Method() != b.Property.Value)
throw new Exception();

b.OC2.Add(o1);
if (b.Method() != b.Property.Value)
throw new Exception();

b.OC2.Add(o2);
if (b.Method() != b.Property.Value)
throw new Exception();
}
}
}