referenceequals

In Effective JAVA by Joshua Bloch, when I was reading about static factory methods , there was a statement as follows The ability of static factory methods to return the same object from repeated invocations allows classes to maintain strict control over what instances exist at any time. Classes that do this are said to be instance-controlled. There are several reasons to write instance-controlled classes. Instance control allows a class to guarantee that it is a singleton (Item 3) or noninstantiable (Item 4). Also, it allows an immutable class (Item 15) to make the guarantee that no two equal

Is the Is VB.NET keyword the same as Object.ReferenceEquals? Yes, it is, unless combined with a TypeOf check. Quote from MSDN: The Is operator determines if two object references refer to the same object. However, it does not perform value comparisons. If object1 and object2 both refer to the exact same object instance, result is True; if they do not, result is False. Is can also be used with the TypeOf keyword to make a TypeOf...Is expression, which tests whether an object variable is compatible with a data type. BTW, also note the IsNot operator (which gives the boolean inverse of the

Why in this situation ReferenceEquals method of object behaves differently? string a= "fg"; string b= "fg"; Console.WriteLine(object.ReferenceEquals(a, b)); So in this situation it's get a result true . In case, it compares values of my strings and not references. But when I write something like: StringBuilder c = new StringBuilder("fg"); string d = c.ToString(); Console.WriteLine(object.ReferenceEquals(a, d)); In this case it works fine and result is false , because it compares references of my objects. Anthony Pegram The first example has a compile time constant "fg" that is referenced by

Is there a default IEqualityComparer<T> implementation that uses ReferenceEquals ? EqualityComparer<T>.Default uses ObjectComparer, which uses object.Equals() . In my case, the objects already implement IEquatable<T> , which I need to ignore and compare by object's reference only. Yurik Just in case there is no default implementation, this is my own: Edit by 280Z28: Rationale for using RuntimeHelpers.GetHashCode(object) , which many of you probably haven't seen before. :) This method has two effects that make it the correct call for this implementation: It returns 0 when the object is null.