Problems defining equals() operator

Question

I have a class

open class Texture

and I'd like to define the equals(other: Texture) operator

operator fun equals(other: Texture) = ...

but I get

Error:(129, 5) Kotlin: 'operator' modifier is inapplicable on this function: must override ''equals()'' in Any

What does it mean?

If I change that to

operator fun equals(other: Any) = ...

Accidental override, two declarations have the same jvm signature

score 8 · Accepted Answer · edited May 23 '17 at 11:48

8

The equals() operator function is defined in Any, so it should be overriden with a compatible signature: its parameter other should be of type Any?, and its return value should be Boolean ~~or its subtype~~ (it's final):

open class Texture {
    // ...

    override operator fun equals(other: Any?): Boolean { ... }
}

Without the override modifier, your function will clash with the Any::equals, hence the accidental override. Also, equals() cannot be an extension (just like toString()), and it cannot be overriden in an interface.

In IntelliJ IDEA, you can use Ctrl+O to override a member, or Ctrl+Insert to generate equals()+hashCode()

edited May 23 '17 at 11:48

Community

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answered Oct 29 '16 at 17:12

hotkey

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Updated the answer due to the update of the question. – hotkey Oct 29 '16 at 17:22
1

How do you arrange for the function to return `false` when `other` is not an instance of `Texture`? – saulspatz Jun 25 '17 at 20:47
1

@saulspatz: I guess the first line lines could be `if (other == null || other !is Texture) return false` – Peter V. Mørch Apr 13 '20 at 10:45

Problems defining equals() operator

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