Adding an Int to a String in scala [duplicate]

Question

I am having a little trouble understanding the rationale behind the following few pieces of scala code:

We all know that 1 + 1 = 2 in the REPL.

scala> 1 + 1
res0: Int = 2

If I type in "Abc" + "Def", I should get "AbcDef" in the REPL.

scala> "Abc" + "Def"
res6: java.lang.String = AbcDef

Now let's say I invoke the + method on String "Abc" and pass "Def" as a parameter:

scala> "Abc".+("Def")
res7: java.lang.String = AbcDef

By the same rationale, why does something like 1.+(1) return a double 2.0?

scala> 1.+(1)
res1: Double = 2.0

Also, why does passing the argument "1" as a parameter result in "1.01" as follows:

scala> 1.+("1")
res9: String = 1.01

Why is the returned result a String instead of an effort for "1" to me transformed into the callers type?

Thanks

Answer 1

If you try that on Scala 2.10.0, you'll get a clue as to the answer:

scala> 1.+(1)
<console>:1: warning: This lexical syntax is deprecated.  From scala 2.11,
             a dot will only be considered part of a number if it is immediately
             followed by a digit.
       1.+(1)
       ^

Simply put, 1. is a valid Double in Scala (as it is in Java), so Scala is really doing this:

1.  +  (1)

That is, infix addition of a Double to an expression enclosed inside a (redundant) parenthesis.

As for the latter, Scala follows Java convention that anything added to a String results in a String and vice versa.