CODEWITHSUNDEEP
scalaoperator-precedence
piyush tripathi
piyush tripathi

Reputation: 117

Operator precedence in scala behaves strange

I was experimenting with operator precedence in Scala, and there is something strange happening here:

class Op{
  def +(that:Op):Op={println("called +");this}
  def -(that:Op):Op={println("called -");this}
  def *(that:Op):Op={println("called *");this}
  def /(that:Op):Op={println("called /");this}
  def %(that:Op):Op={println("called %");this}
}

val op = new Op;
op+op-op*op/op%op ;
op+op*op ;

For the first line, the output is:

called +
called *
called /
called %
called -

(Notice + is called before *.) However, for the second line, the output is:

called *
called +

(* is called before +.) I believe from what I read here that * should be called before +. Is there something I got wrong?

Upvotes: 0

Views: 79

Answers (1)

0__
0__

Reputation: 67330

Scala groups the expression by precedence, then evaluates the groups strictly from left to right, thus adhering to the precedence.

Your second call is equivalent to

op.+(op.*(op))

which is evaluated from inside to outside.

The same with the first call:

op+op-op*op/op%op

which becomes, with precedence applied,

op+op-(op*op/op%op)

or

(op+op).-(op*op/op%op)

or

// 1     5    2     3     4
op.+(op).-(op.*(op)./(op).%(op))

Upvotes: 4

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