swift - Automatic Type Conversion with extension: What is happening here? -

i'm going through first chapter of the swift programming language book , i'm @ part it's describing extension keyword.

i had go @ "experiment":

“write extension double type adds absolutevalue property.”

i got working this:

extension double {     var absolutevalue: double {         if(self < 0) {             return self * -1         }          return self     } }  (-10.5).absolutevalue    // 10.5 

but seems work integers:

(-4).absolutevalue       // 4.0 

what happening here? compiler changing type int double because sees there absolutevalue extension on double not int?

this appears case because if add extension of same name on int so:

extension int {     var absolutevalue: int {         return 42     } } 

that overrides extension on double. , (-4).absolutevalue returns 42

is there way add extension only works on doubles not ints?

edit: looks it's doing conversion @ compile-time , since didn't define type literal converted it. following produces error

var i:int = -4; i.absolutevalue 

"playground execution failed: error: :12:1: error: 'int' not have member named 'absolutevalue' i.absolutevalue ^ ~~~~~~~~~~~~~"

edit 2: appears apply literals; following produces error:

var = -4; i.absolutevalue 

yes, extension wrote doubles, not ints. take @ example:

extension double {     var absolutevalue: double {         if (self < 0) {             return self * -1         }          return self     } }  var double: int = 10 double.absolutevalue // int not have member named absolutevalue 

but, in code compiler implicitly converting int double.