Replace TrimmedString regex with Trimmed predicate type

This also adds `TrimmedString.trim` and is a replacement for fthomas#487 based
on the discussion there.

modules/core/shared/src/main/scala/eu/timepit/refined/string.scala

@@ -69,6 +69,9 @@ object string extends StringInference {
   /** Predicate that checks if a `String` is a valid XPath expression. */
   final case class XPath()
 
+  /** Predicate that checks if a `String` has no leading or trailing whitespace. */
+  final case class Trimmed()
+
   object EndsWith {
     implicit def endsWithValidate[S <: String](
         implicit ws: Witness.Aux[S]): Validate.Plain[String, EndsWith[S]] =
@@ -234,6 +237,11 @@ object string extends StringInference {
         XPath()
       )
   }
+
+  object Trimmed {
+    implicit def trimmedValidate: Validate.Plain[String, Trimmed] =
+      Validate.fromPredicate(s => s.trim == s, t => s"$t is trimmed", Trimmed())
+  }
 }
 
 private[refined] trait StringInference {

modules/core/shared/src/main/scala/eu/timepit/refined/types/string.scala

@@ -3,7 +3,7 @@ package eu.timepit.refined.types
 import eu.timepit.refined.W
 import eu.timepit.refined.api.{Refined, RefinedType, RefinedTypeOps}
 import eu.timepit.refined.collection.{MaxSize, NonEmpty}
-import eu.timepit.refined.string.MatchesRegex
+import eu.timepit.refined.string.{MatchesRegex, Trimmed}
 import shapeless.Witness
 
 /** Module for `String` refined types. */
@@ -52,9 +52,13 @@ object string {
   object NonEmptyString extends RefinedTypeOps[NonEmptyString, String]
 
   /** A `String` that contains no leading or trailing whitespace. */
-  type TrimmedString = String Refined MatchesRegex[W.`"""^(?!\\s).*(?<!\\s)"""`.T]
+  type TrimmedString = String Refined Trimmed
 
-  object TrimmedString extends RefinedTypeOps[TrimmedString, String]
+  object TrimmedString extends RefinedTypeOps[TrimmedString, String] {
+
+    /** Creates a `TrimmedString` from `s` by trimming it. */
+    def trim(s: String): TrimmedString = Refined.unsafeApply(s.trim)
+  }
 
   /** A `String` representing a hexadecimal number */
   type HexStringSpec = MatchesRegex[W.`"""^(([0-9a-f]+)|([0-9A-F]+))$"""`.T]

modules/core/shared/src/test/scala/eu/timepit/refined/types/StringTypesSpec.scala

@@ -35,6 +35,11 @@ class StringTypesSpec extends Properties("StringTypes") {
     (truncated.value ?= str.take(FString3.maxLength))
   }
 
+  property("""TrimmedString.trim(str)""") = forAll { (str: String) =>
+    val trimmed = TrimmedString.trim(str)
+    TrimmedString.from(str) ?= Right(trimmed)
+  }
+
   // Hashes for ""
   object EmptyString {
     val md5 = "d41d8cd98f00b204e9800998ecf8427e"

scalastyle-config.xml

@@ -42,7 +42,7 @@
  </check>
  <check level="error" class="org.scalastyle.scalariform.NumberOfTypesChecker" enabled="true">
   <parameters>
-   <parameter name="maxTypes"><![CDATA[40]]></parameter>
+   <parameter name="maxTypes"><![CDATA[45]]></parameter>
   </parameters>
  </check>
  <check level="error" class="org.scalastyle.scalariform.CyclomaticComplexityChecker" enabled="true">