Implicit parameters

An implicit parameter is an actual parameter, which is a value passed to a function (or method) in a function (or method) call. When a method (or function) has an implicit parameter, it's up to the developer to pass it explicitly, or make it available in the current scope to pass it automatically to the Scala compiler.

Consider the following example:

scala> def add(x: Int, implicit y: Int) = x + y 
<console>:1: error: identifier expected but 'implicit' found. 
       def add(x: Int, implicit y: Int) = x + y 
                       ^ 
 
scala> def add(x: Int) (implicit y: Int) = x + y 
add: (x: Int)(implicit y: Int)Int 
 
scala> add(11) 
<console>:15: error: could not find implicit value for parameter y: Int 
       add(11) 
          ^ 
 
scala> implicit a:Int = 12 
<console>:1: error: expected start of definition 
       implicit a:Int = 12 
                ^ 
 
scala> implicit val a:Int = 12 
a: Int = 12 
 
scala> add(11) 
res1: Int = 23