Reference equality for java.lang.String in Scala
equality, reference, referenceequals, scala, string
Solution
Yes it's compiler magic. Specifically, it's called interning. Java does it as well, and it's simply for efficiency reasons, such as memory usage and allowing comparisons without comparing every character. Here's a Wikipedia article on it. You can also intern Strings manually with the `intern()` method.
Problem
One would expect that even though strings are immutable, value-equality and reference-equality would not be the same for java.lang.String objects in Scala. This means that two string-holding `val`s should not be reference-equal even when their strings are identical. But here's what I get in a 2.9.1.final REPL: ``` scala> val s1 = "a"; val s2 = "a" s1: java.lang.String = a s2: java.lang.String = a scala> s1 eq s2 res0: Boolean = true ``` Any idea why the result was not `false`? The same experiment with `List("a")` instead of `"a"` works as expected. The `eq` method is marked as final in AnyRef. Is there any compiler magic done specifically for `String` or `java.lang.String`?