scalaequals

ScalaEquals

ScalaEquals provides easy to use macros for generating correct equals/hashCode/canEquals implementations, never look up an equals/hashCode recipe again! The methods generated from ScalaEquals are taken directly from Programming in Scala* and strictly obey the contract of equals:

• Reflexive
• Symmetric
• Transitive

As well as the additional properties that equals is consistent (x.equals(y) consistently returns one of true or false) and that for any non-null value x, x.equals(null) always returns false. Additionally, using ScalaEquals.hash will guarantee that hashCode() is always consistent with equals. In the documentation, anywhere ScalaEquals.equal is seen it is assumed that ScalaEquals.equalAllVals also applies, unless otherwise stated. Additionally, in the documentation the argument names are assumed to be other, but this is not a requirement, you may name the parameters however you would like.

The typical use case is as follows:

class Point(val x: Int, val y: Int) {
    override def equals(other: Any): Boolean = ScalaEquals.equal
    override def hashCode(): Int = ScalaEquals.hash
    def canEquals(other: Any): Boolean = ScalaEquals.canEquals
    override def toString: String = ScalaEquals.genString
}

// After macro expansion, the above is converted to:

class Point(val x: Int, val y: Int) {
     override def equals(other: Any): Boolean = other match {
       case that: Point => (that canEquals this) && that.x == this.x && that.y == this.y
       case _ => false
     }
     override def hashCode(): Int = MurmurHash3.seqHash(List(x, y))
     def canEquals(other: Any): Boolean = other.isInstanceOf[Point]
     override def toString: String = "Point(" + x + ", " + y + ")"
}

Things to note:

• The macros will intelligently pick other methods to call. Specifically, if the class extends a class that also override equals, super.equals(that) will be called. If canEquals is not defined, it will not be added to the equals call. ScalaEquals.hash will call super.hashCode() if and only if super.equals(that) is called.
• The macros may only be called from their respectively named methods, ScalaEquals.equal can only be called in a method named equals. ScalaEquals.hash can only be called in a method named hashCode(). ScalaEquals.canEquals can only be called in a method name canEquals. This serves as a safety net to ensure these methods are never called somewhere they are not supposed to be.

See the github readme for more information. Also, see org.scalaequals.ScalaEquals for additional examples.

* Programming in Scala by Martin Odersky, Lex Spoon and Bill Venners, Artima Press, 2008: Chapter 28 (Object equality) / Second Edition, 2011: Chapter 30 (Object equality)