ReferenceEquals working wrong with strings

The first example has a compile time constant "fg" that is referenced by two variables. Since this is a compile time constant, the two variables reference the one object. The references are equal.

Read into the topic of string interning for more on this behavior. As a starter, consider:

For example, if you assign the same literal string to several variables, the runtime retrieves the same reference to the literal string from the intern pool and assigns it to each variable.

http://msdn.microsoft.com/en-us/library/system.string.intern.aspx

In the second example, only one is a compile time constant, the other is a result of some operations. a and d do not reference the same object, so you get the false result from ReferenceEquals.

It is behaving correctly in both cases.

The reason a and b are the same string object is because the compiler has noticed that you specified the same string twice, and has reused the same string object to initialize both a and b.

This will generally happen with every string constant in your application.