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Why Everyone Hates Operator Overloading

· Java Zone

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… no, don’t tell me you like Perl. Because you don’t. You never did. It does horrible things. It makes your code look like…

Perl made heavy use of operator overloading and used operators for a variety of things. A similar tendency can be seen in C++ and Scala. See also people comparing the two. So what’s wrong with operator overloading?

People never agreed whether Scala got operator overloading right or wrong:

Usually, people then cite the usual suspects, such as complex numbers (getting things right):

class Complex(val real:Int, val imaginary:Int) {
  def +(operand:Complex):Complex = {
    new Complex(real + operand.real, imaginary + operand.imaginary)

  def *(operand:Complex):Complex = {
    new Complex(real * operand.real - imaginary * operand.imaginary,
      real * operand.imaginary + imaginary * operand.real)

The above will now allow for adding and multiplying complex numbers, and there’s absolutely nothing wrong with that:

val c1 = new Complex(1, 2)
val c2 = new Complex(2, -3)
val c3 = c1 + c2
val res = c1 + c2 * c3

But then, there are these weirdo punctuation things that make average programmers simply go mad:


Don't believe it? Check out this graph library!

To the above, we say:

Operator Overloading? Meh

How operator overloading should be

Operator overloading can be good, but mostly isn’t. In Java, we’re all missing better ways to interact with BigDecimal and similar types:

// How it is:
// How it should be:
bigdecimal1 + bigdecimal2 * bigdecimal3

Of course, operator precedence would take place as expected. Unlike C++ or Scala, ideal operator overloading would simply map common operators to common method names. Nothing more. No one really wants API developers to come up with fancy ##-%>> operators.

While CeylonGroovy, and Xtend implemented this in a somewhat predictable and useful way, Kotlin is probably the language that has implemented the best standard operator overloading mechanism into their language. Their documentation states:

Binary operations

a + b a.plus(b)
a – b a.minus(b)
a * b a.times(b)
a / b a.div(b)
a % b a.mod(b)
a..b a.rangeTo(b)

That looks pretty straightforward. Now check this out:

“Array” access

a[i] a.get(i)
a[i, j] a.get(i, j)
a[i_1, ..., i_n] a.get(i_1, …, i_n)
a[i] = b a.set(i, b)
a[i, j] = b a.set(i, j, b)
a[i_1, ..., i_n] = b a.set(i_1, …, i_n, b)

Now, I really don’t see a single argument against the above. This goes on, and unfortunately, Java 8 has missed this train, as method references cannot be assigned to variables and invoked like JavaScript functions(although, that’s not too late for Java 9+):

Method calls

a(i) a.invoke(i)
a(i, j) a.invoke(i, j)
a(i_1, …, i_n) a.invoke(i_1, …, i_n)

Simply beautiful!


We’ve recently blogged about Ceylon’s awesome language features. But the above Kotlin features are definitely a killer and would remove any other sorts of desires to introduce operator overloading in Java for good.

Let’s hope future Java versions take inspiration from Kotlin, a language that got operator overloading right.

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Published at DZone with permission of Lukas Eder, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

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