Typesafe equality and contains checking in ScalaTest

gistfile1.txt

scala> import org.scalautils._
import org.scalautils._

scala> import org.scalatest._
import org.scalatest._

scala> import Matchers._
import Matchers._

scala> import TypeCheckedTripleEquals._
import TypeCheckedTripleEquals._

scala> val xs = List(1, 2, 3)
xs: List[Int] = List(1, 2, 3)

scala> val ys = List("1", "2", "3")
ys: List[String] = List(1, 2, 3)

// You can get equality checks with type checking via ===:

scala> xs should === (ys)
<console>:25: error: types List[Int] and List[String] do not adhere to the type constraint selected for the === and !== operators; the missing implicit parameter is of type org.scalautils.Constraint[List[Int],List[String]]
              xs should === (ys)
                 ^

// Just using contain does not give you a type error, because contain can be used with and,
// or, and not in matcher compositions. I decided that carrying a type constrait along
// for the ride in logical expressions would make the user code harder to understand than
// the benefit of type errors versus test failures:

scala> xs should contain ("1")
org.scalatest.exceptions.TestFailedException: List(1, 2, 3) did not contain element "1"
	at org.scalatest.MatchersHelper$.newTestFailedException(MatchersHelper.scala:160)
	at org.scalatest.Matchers$ShouldMethodHelper$.shouldMatcher(Matchers.scala:5980)
	...

// If you want a type error for contains checking, you should use inspectors 
// or inspector shorthands instead. Here's an example:

scala> atLeast (1, xs) should === ("1")
<console>:24: error: types Int and String do not adhere to the type constraint selected for the === and !== operators; the missing implicit parameter is of type org.scalautils.Constraint[Int,String]
              atLeast (1, xs) should === ("1")
                              ^

// In the contain case, it works for more than just equality checks. Here you
// get a type error checking to see if a list of strings contains an Int greater
// than 7

scala> atLeast (1, ys) should be > 7
<console>:24: error: overloaded method value should with alternatives:
  (fullyMatchWord: org.scalatest.words.FullyMatchWord)org.scalatest.Matchers.ResultOfFullyMatchWordForCollectedString <and>
  (includeWord: org.scalatest.words.IncludeWord)org.scalatest.Matchers.ResultOfIncludeWordForCollectedString <and>
  (endWithWord: org.scalatest.words.EndWithWord)org.scalatest.Matchers.ResultOfEndWithWordForCollectedString <and>
  (startWithWord: org.scalatest.words.StartWithWord)org.scalatest.Matchers.ResultOfStartWithWordForCollectedString <and>
  (notWord: org.scalatest.words.NotWord)org.scalatest.Matchers.ResultOfNotWordForCollectedString <and>
  (notExist: org.scalatest.words.ResultOfNotExist)(implicit existence: org.scalatest.enablers.Existence[String])Unit <and>
  (existWord: org.scalatest.words.ExistWord)(implicit existence: org.scalatest.enablers.Existence[String])Unit <and>
  (containWord: org.scalatest.words.ContainWord)org.scalatest.Matchers.ResultOfContainWordForCollectedAny[String] <and>
  (inv: org.scalautils.TripleEqualsSupport.TripleEqualsInvocationOnSpread[String])(implicit ev: Numeric[String])Unit <and>
  [U](inv: org.scalautils.TripleEqualsSupport.TripleEqualsInvocation[U])(implicit constraint: org.scalautils.Constraint[String,U])Unit <and>
  (haveWord: org.scalatest.words.HaveWord)org.scalatest.Matchers.ResultOfHaveWordForCollectedExtent[String] <and>
  (beWord: org.scalatest.words.BeWord)org.scalatest.Matchers.ResultOfBeWordForCollectedAny[String] <and>
  [TYPECLASS1[_], TYPECLASS2[_]](rightMatcherFactory2: org.scalatest.matchers.MatcherFactory2[String,TYPECLASS1,TYPECLASS2])(implicit typeClass1: TYPECLASS1[String], implicit typeClass2: TYPECLASS2[String])Unit <and>
  [TYPECLASS1[_]](rightMatcherFactory1: org.scalatest.matchers.MatcherFactory1[String,TYPECLASS1])(implicit typeClass1: TYPECLASS1[String])Unit <and>
  (rightMatcher: org.scalatest.matchers.Matcher[String])Unit
 cannot be applied to (org.scalatest.matchers.Matcher[Int])
              atLeast (1, ys) should be > 7
                              ^

// Inspectors are described here:

http://doc.scalatest.org/2.0/index.html#org.scalatest.Inspectors

// Inspector shorhands are described here:

http://doc.scalatest.org/2.0/index.html#org.scalatest.Matchers@inspectorShorthands

// TypeCheckedTripleEquals is desribed here:

http://doc.scalatest.org/2.0/index.html#org.scalatest.Matchers@inspectorShorthands