Scala implicit class restriction

Question

Scala documentation states that implicit class "must be defined inside of another trait/class/object"

What is the reason for this constraint?

Answer 1

The referenced SIP describes implicit classes as being syntactic sugar for a class and a def .

Annotations on implicit classes default to attaching to the generated class and the method. For example,

 @bar implicit class Foo(n: Int) 

will desugar into:

 @bar implicit def Foo(n: Int): Foo = new Foo(n) @bar class Foo(n:Int) 

Since a def must be within a trait/class/object, an implicit class, being partially "composed of" a def , must also obey this condition.