问题
When I invoke + on 2 I get an Int back, but when its done using explicit method call I get Double instead.
scala> 2+2
res1: Int = 4
scala> 2.+(2)
res2: Double = 4.0
It seems that .+() is invoked on implicit converted Int to Double.
scala> 2.+
<console>:16: error: ambiguous reference to overloaded definition,
both method + in class Double of type (x: Char)Double
and method + in class Double of type (x: Short)Double
match expected type ?
2.+
^
Why is that so ?
回答1:
The reason is not in explicit method call -- by writing 2.+ you specifying Double on the left side and then calling addition operator on it:
scala> 2.
res0: Double = 2.0
回答2:
In Scala 2.9 and before, 2. is interpreted as 2.0 so the ambiguous dot denotes a float literal. You’d explicitly call the method by using the syntax (2).+(2).
The ambiguous floating point syntax will however be deprecated in 2.10:
scala> 2.+(2)
<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.
2.+(2)
^
<console>:2: 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.
2.+(2)
^
<console>:8: 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.
2.+(2)
^
res1: Double = 4.0
来源：https://stackoverflow.com/questions/9655080/scala-operator-oddity