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README.md

ScalaEquals

ScalaEquals provides easy to use macros for generating correct equals/hashCode/canEqual 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 and hashCode, and unlike case classes, the generated methods work as expected with sub-classing. As a bonus, the macros also check that equals/hashCode/canEqual/toString are defined correctly; they will catch misspellings, incorrect types, etc.

In the documentation and in this README, 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 macros will find the name of the parameter and use it in the expansion.

Downloading

You can download ScalaEquals directly from Sonatype, or to use with sbt, add the following to your project file:

libraryDependencies += "org.scalaequals" %% "scalaequals-core" % "1.2.0"

How To Use

Equals Using All vals In Constructor

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

Equals Using All vals In Constructor And Body

// TIP: Statically importing ScalaEquals will make the methods look even cleaner!
import org.scalaequals.ScalaEquals._
class Point(_x: Int, val y: Int) {
  val x: Int = _x
  override def equals(other: Any): Boolean = equalAllVals
  override def hashCode(): Int = hash
  def canEqual(other: Any): Boolean = canEquals
  override def toString: String = genString                          // returns "Point(_x, y)"
}

Equals Using User-Defined Fields

import org.scalaequals.ScalaEquals._
import org.scalaequals.ScalaEqualsExtend
class Point(_x: Int, var y: Int) {
  def x: Int = _x
  override def equals(other: Any): Boolean = ScalaEqualsExtend.equal(x, y)
  override def hashCode(): Int = hash
  def canEqual(other: Any): Boolean = canEquals
  override def toString: String = genString(x, y)                    // returns "Point(x, y)"
}

Details

  • Every equal method will use canEqual if it is defined.

  • Every equal method will use super.equals(that) if a super class that is not AnyRef or Object overrides equals.

  • ScalaEquals.equal will use all vals in constructor that are not inherited from a parent class, i.e. val, protected val, private val, but not anything qualified with override.

  • ScalaEquals.equalAllVals will use all vals in constructor AND body of class, subject to the same constraints as above.

  • ScalaEqualsExtend.equal(params) will use only the fields specified in params (as well as super.equals if applicable). Valid arguments include val, var, lazy val, and def that take no arguments. Any access modifier is allowed, and unlike equal and equalAllVals, arguments inherited from a super class and/or qualified with override may also be used. Use at your own risk

  • ScalaEquals.hash will use exactly the values checked in equals

  • ScalaEquals.hash will use super.hashCode() if and only if super.equals(that) is called in equals.

  • ScalaEquals.hash will work with lazy hashCode, i.e. - override lazy val hashCode: Int = ScalaEquals.hash

  • ScalaEquals.canEquals is a simple macro that converts to other.isInstanceOf[Class]

  • ScalaEquals.genString uses all constructor parameters in the generated string. ScalaEquals.genString(params) works identically to ScalaEquals.equal(params).

  • Works with classes, traits, abstract classes and generic variants (parameterized and with abstract type members). As always, be careful about initialization order when using traits and abstract classes.

  • ScalaEqualsExtend contains various additional flavors of the equals/hashCode macros that if used incorrectly will not produce implementations that obey the contract. Use at your own risk.

  • Use -Xmacro-settings:scala-equals-no-warn to silence warnings from macros.

Example Macro Expansion

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

becomes

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

Additional Features

Equals Without Using compareTo for Double/Float values

ScalaEqualsExtend.equalNoCompareTo
ScalaEqualsExtend.equalAllValsNoCompareTo
ScalaEqualsExtend.equalNoCompareTo(param, params...)

Hash using a custom hash function of type Array[Any] => Int

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

Feedback

Questions or Comments?

Want to tell me how awesome (or horrible) ScalaEquals is? Send me an email!

Found a Bug? Want a New Feature?

Add issues or feature requests here on github at the issue tracker, alternatively fork the project and submit a pull request.

Release Notes

View complete release notes.

Equals Contract

It is reflexive: for any non-null value x, the expression x.equals(x) should return true.

It is symmetric: for any non-null values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.

It is transitive: for any non-null values x, y, and z, if x.equals(y) re-turns true and y.equals(z) returns true, then x.equals(z) should return true.

It is consistent: for any non-null values x and y, multiple invocations of x.equals(y) should consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.

• For any non-null value x, x.equals(null) should return false.

• For any non-null values x and y, if x.equals(y) returns true then x.hashCode() == y.hashCode() should return true.

Testing

All implementations have been thoroughly tested using ScalaCheck. Check out the core-test project for details, specifically check out the documentation for EqualsFixture for exact testing methodology. If you find a problem, please submit an issue! As always, even when the implementation is perfect, it is good to sanity check your own code to ensure that the logic of equals/hashCode is defined how you want it to be.

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