Why is reading a settings property value making a SettingsPropertyValue object dirty?

Question

While implementing a custom settings provider I noticed that accessing a setting property's value changes its IsDirty flag to true.

// Arrange
var property = new SettingsProperty("property1")
{
    PropertyType = typeof(Color),
    DefaultValue = "Green"
};

// Act
var result = new SettingsPropertyValue(property);

// Assert
Assert.That(result.IsDirty, Is.False);
Assert.That(result.PropertyValue, Is.EqualTo(Color.Green));
Assert.That(result.IsDirty, Is.False); // <-- Assertion fails

Reflector gives me an answer to the question why the PropertyValue getter is behaving like this - it contains a statement like the following:

if (_Value != null && !Property.PropertyType.IsPrimitive && !(_Value is string) && !(_Value is DateTime))
{
    _UsingDefaultValue = false;
    _ChangedSinceLastSerialized = true;
    _IsDirty = true;
}

Can anybody shed some light on this at first glance strange behavior?

Answer 1

The documentation states that this is to account for any potential side effects of accessing the value when it is a complex type, as well as mutating the value without reassigning the value (for example when modifying the items in a list):

The IsDirty property is set to true under the following conditions:

1. [...]

2. The value contained in the SettingsPropertyValue object is accessed, and the value is not a string or a primitive type such as int, float, real, or DateTime. When the value managed by a SettingsPropertyValue object is a complex type (for example an ArrayList), there is no way for a SettingsPropertyValue object to detect when changes have been made. As a result, the SettingsPropertyValue object pessimistically assumes that a complex type is dirty once it has been accessed from the PropertyValue property.