String interning?

Question

The second ReferenceEquals call returns false. Why isn\'t the string in s4 interned? (I don\'t care about the advantages of StringBuilder over string concatenation.)

Answer 1

Strings are immutable. This means their contents can't be changed.

When you do s4 += "m"; internally, the CLR copies the string to another location in memory which contains the original string and the appended part.

See MSDN string reference.