Scalactic

<!DOCTYPE html> <html> <head> <meta http-equiv="content-type" content="text/html;charset=utf-8" /> <title>Scalactic</title> <link rel="Stylesheet" href="/assets/stylesheets/main.css" type="text/css" media="screen"/>  <script async src="https://www.googletagmanager.com/gtag/js?id=G-19BZD1XMRV"></script> <script defer src='/assets/javascripts/gtag.js'></script> </head> <body> <div class="Container">  <script id="adsArtimaScript" type="text/javascript" src="https://www.artima.com/assets/javascripts/4ca150665e51d0b1c3890ca1b891c507-ads.js?product=Scalactic"></script> <div id="Header"> <div id="Nav"> <a href="/">Home</a> | <span><em>Quick Start</em></span> | <a href="/install">Install</a> | <a href="/user_guide">User Guide</a> | <a href="/scaladoc">Scaladoc</a> | <a href="/supersafe">SuperSafe</a> | <a href="/about">About</a> </div>  </div>  <div id="body"> <div class="message"> <a class="scalatestLogo" href="./"> <img src="/assets/images/scalacticLogo.gif" width="400" height="60" alt="ScalaTest"/> </a> </div> <div style="text-align: left"> <h1>Scalactic quick start</h1> <p> A good way to get started with Scalactic is to try out its type-checking <code>===</code> operator in the Scala interpreter. First start Scala 3, including <a href="https://oss.sonatype.org/content/groups/public/org/scalactic/scalactic_3/3.2.19/scalactic_3-3.2.19.jar">this Scalactic Jar file</a> on the classpath: </p> <pre class="scala"> $ scala -cp scalatest_3-3.2.19.jar Welcome to Scala version 3.3.3 (...). Type in expressions to have them evaluated. Type :help for more information. </pre> <p> Copy and paste this code into the interpreter: </p> <pre class="stHighlighted"> import org.scalactic._ import TypeCheckedTripleEquals._ Some(1) === 2 Some(1) === Some(2) 1 === 1L import ConversionCheckedTripleEquals._ 1 === 1L List(1, 2, 3) === Vector(1, 2, 3) import TraversableEqualityConstraints._ List(1, 2, 3) === Vector(1, 2, 3) List(1, 2, 3) === Set(1, 2, 3) </pre> <p> You should see the output shown below. By importing the members of <code>org.scalactic.TypeCheckedTripleEquals</code>, you get a <code>===</code> operator that requires the left- and right-hand types to be a subtype and/or supertype of each other: </p> <pre class="scala"> scala> import org.scalactic._ import org.scalactic._ scala> import TypeCheckedTripleEquals._ import TypeCheckedTripleEquals._ </pre> <p> For example, in the following expression because the left-hand type, <code>Some[Int]</code>, and the right-hand type, <code>Int</code>, are not in a subtype/supertype relationship, you'll get a compiler error: </p> <pre class="scala"> scala> Some(1) === 2 <console>:14: error: types Some[Int] and Int do not adhere to the type constraint selected for the === and !== operators; the missing implicit parameter is of type org.scalactic.Constraint[Some[Int],Int] Some(1) === 2 ^ </pre> <p> By contrast, in the following expression both the left- and right-hand types are <code>Some[Int]</code>. Because a type is a subtype and supertype of itself, the code compiles (and at runtime yields false): </p> <pre class="scala"> scala> Some(1) === Some(2) res1: Boolean = false </pre> <p> However, because <code>Int</code> and <code>Long</code> are not in a subtype/supertype relationship, the following will generate a compiler error, even though if this were allowed to compile, it would yield <code>true</code>: </p> <pre class="scala"> scala> 1 === 1L <console>:14: error: types Int and Long do not adhere to the type constraint selected for the === and !== operators; the missing implicit parameter is of type org.scalactic.Constraint[Int,Long] 1 === 1L ^ </pre> <p> The previous expression would yield <code>true</code> if allowed to compile because the <code>Int</code> would be implicitly widened to <code>Long</code> via an implicit conversion in <code>scala.Predef</code>. Importing the members of <code>ConversionCheckedTripleEquals</code> will give you a <code>===</code> operator that requires that either the left- and right-hand types to be a subtype or supertype of each other, or an implicit conversion exists in one direction or the other: </p> <pre class="scala"> scala> import ConversionCheckedTripleEquals._ import ConversionCheckedTripleEquals._ </pre> <p> Now the same expression compiles and yields <code>true</code>: </p> <pre class="scala"> scala> 1 === 1L res3: Boolean = true </pre> <p> The following expression does <em>not</em> compile, however, because <code>List[Int]</code> and <code>Vector[Int]</code> are not a subtype or supertype of each other, and no implicit conversion exists between them: </p> <pre class="scala"> scala> List(1, 2, 3) === Vector(1, 2, 3) <console>:17: error: types List[Int] and scala.collection.immutable.Vector[Int] do not adhere to the type constraint selected for the === and !== operators; the missing implicit parameter is of type org.scalactic.Constraint[ List[Int], scala.collection.immutable.Vector[Int]] List(1, 2, 3) === Vector(1, 2, 3) ^ </pre> <p> Importing the members of <code>TraversableEqualityConstraints</code>s provides additional implicits that enable equality comparisons of collections that make sense for Scala. For example, any subtype of <code>GenSeq</code> can be compared with any other subtype of <code>GenSeqs</code>: </p> <pre class="scala"> scala> import TraversableEqualityConstraints._ import TraversableEqualityConstraints._ scala> List(1, 2, 3) === Vector(1, 2, 3) res5: Boolean = true </pre> <p> In addition, subtypes of <code>GenSet</code> can be compared with each other, as can subtypes of <code>GenMap</code>. But an attempt to compare a <code>Seq</code> with a <code>Set</code> for equality won't compile, because it would always yield <code>false</code>: </p> <pre class="scala"> scala> List(1, 2, 3) === Set(1, 2, 3) <console>:20: error: types List[Int] and scala.collection.immutable.Set[Int] do not adhere to the type constraint selected for the === and !== operators; the missing implicit parameter is of type org.scalactic.Constraint[ List[Int], scala.collection.immutable.Set[Int]] List(1, 2, 3) === Set(1, 2, 3) ^ </pre> <p> In short, Scalactic's type-checking <code>===</code> operator provides you with a tunable type check for equality comparisons. For more information, see the documentation for <a href='/scaladoc/3.2.19/org/scalactic/TypeCheckedTripleEquals.html'><code>TypeCheckedTripleEquals</code></a>, <a href='/scaladoc/3.2.19/org/scalactic/ConversionCheckedTripleEquals.html'><code>ConversionCheckedTripleEquals</code></a>, and <a href='/scaladoc/3.2.19/org/scalactic/TraversableEqualityConstraints.html'><code>TraversableEqualityConstraints</code></a>. </p> <p> Like ScalaTest, Scalactic consists if discrete traits so that you can import only the implicits you need, minimizing potential conflicts and maximizing compiler speed. If you decide you'll want certain features of Scalactic generally, you can mix them into a singleton object and just import its members. Here's an example: </p> <pre class="stHighlighted"> <span class="stReserved">package</span> com.mycompany.myproject <span class="stReserved">import</span> org.scalactic._ <span class="stReserved">object</span> <span class="stType">OurScalactic</span> <span class="stReserved">extends</span> <span class="stType">TypeCheckedTripleEquals</span> <span class="stReserved">with</span> <span class="stType">TraversableEqualityConstraints</span> <span class="stReserved">with</span> <span class="stType">Tolerance</span> <span class="stReserved">with</span> <span class="stType">Explicitly</span> <span class="stReserved">with</span> <span class="stType">TimesOnInt</span> </pre> <p> You can now import your desired Scalactic functionality in one line: </p> <pre class="stHighlighted"> <span class="stReserved">package</span> com.mycompany.myproject <span class="stReserved">import</span> OurScalactic._ <span class="stLineComment">// Your code here</span> </pre> <p> To include Scalactic in your sbt project, simply add this line: </p> <pre class="stHighlighted"> libraryDependencies += <span class="stQuotedString">"org.scalactic"</span> % <span class="stQuotedString">"scalactic_3"</span> % <span class="stQuotedString">"3.2.19"</span> </pre> <p> To include Scalactic in your Maven project, use: </p> <pre class="stHighlighted"> <dependency> <groupId>org.scalactic</groupId> <artifactId>scalactic_3</artifactId> <version>3.2.19</version> </dependency> </pre> <p> You are off and running! For more information, consult the <a href="/user_guide">user guide</a>. </p> </div> </div>  <div style="font-size: 66%; margin-top: 60px"> <p> Scalactic is brought to you by Bill Venners, with contributions from several other folks. It is sponsored by Artima, Inc.<br /> ScalaTest is free, open-source software released under the <a href="http://www.apache.org/licenses/LICENSE-2.0.html">Apache 2.0 license</a>. </p> <p> Copyright © 2009-2025 Artima, Inc. All Rights Reserved. </p> <p> <a href="http://www.artima.com" class="no_link_hover"> <img src="/assets/images/artima100Black.png" style="margin-top: 2px" width="100" height="38" alt="artima"/> </a> </p> </div>  </div>  </body> </html>

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Scalactic