What are all the instances of syntactic sugar in Scala?

Question

What are all the instances of syntactic sugar in Scala?

They are hard to search for since most/all of them are purely symbols and are thus hard to search for without knowing the name of the concept.

TODO:

• Implicit conversions
• _ syntax for anonymous functions
• Other things I'm forgetting

Answer 1

Basics:

• a b is equivalent to a.b.
• a b c is equivalent to a.b(c), except when b ends in :. In that case, a b c is equivalent to c.b(a).

• a(b) is equivalent to a.apply(b) This is why the following definitions for an anonymous functions are identical:

  val square1 = (x: Int) => x*x
  val square2 = new Function1[Int,Int] {
      def apply(x: Int) = x*x
  }
  

  When calling square1(y), you are actually calling square1.apply(y) which square1 must have as specified by the Function1 trait (or Function2, etc...)

• a(b) = c is equivalent to a.update(b,c). Likewise, a(b,c) = d is equivalent to a.update(b,c,d) and so on.

• a.b = c is equivalent to a.b_=(c). When you create a val/var x in a Class/Object, Scala creates the methods x and x_= for you. You can define these yourself, but if you define y_= you must define y or it will not compile, for example:

  scala> val b = new Object{ def set_=(a: Int) = println(a) }
  b: java.lang.Object{def set_=(Int): Unit} = $anon$1@17e4cec
  
  scala> b.set = 5
  <console>:6: error: value set is not a member of java.lang.Object{def set_=(Int): Unit}
         b.set = 5
           ^
  
  scala> val c = new Object{ def set = 0 ; def set_=(a:Int) = println(a) }
  c: java.lang.Object{def set: Int; def set_=(Int): Unit} = $anon$1@95a253
  
  scala> c.set = 5
  5
  

• -a corresponds to a.unary_-. Likewise for +a,~a, and !a.

• a <operator>= b, where <operator> is some set of special characters, is equivalent to a = a <operator> b only if a doesn't have the <operator>= method, for example:

  class test(val x:Int) {
      def %%(y: Int) = new test(x*y)
  }
  
  var a = new test(10)
  a.x // 10
  a %%= 5 // Equivalent to a = a %% 5
  a.x // 50