What are all the instances of syntactic sugar in Scala?

In addition to Jaxkson's answer:

• type F[A,B] can be used as A F B.

For example:

type ->[A,B] = (A,B)
def foo(f: String -> String)

• Using => type in a method definition makes the compiler wrap expressions inside the method call in a function thunk.

For example

def until(cond: => Boolean)(body: => Unit) = while(!cond) body

var a = 0
until (a > 5) {a += 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
  

Special Classes: Tuples and Symbols

As mentioned by Rahul G, tuples and symbols get a slightly special syntax.

• Symbols: the syntax 'x is short for Symbol("x")
• Tuples: (p1,p2,..,pn) is short for a case class Tuplen[T1,T2,..,Tn](p1,p2,..,pn)

For example, the following two are equivalent.

val tuple1 = ("Hello",1)
val tuple2 = Tuple2[String,Int]("Hello",1)