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copied!<p>The reason why there occur differences is documented in ScalaDoc.</p> <p>WrappedString:</p> <blockquote> <p>The difference between this class and <code>StringOps</code> is that calling transformer methods such as <code>filter</code> and <code>map</code> will yield an object of type <code>WrappedString</code> rather than a <code>String</code>.</p> </blockquote> <p>StringOps:</p> <blockquote> <p>The difference between this class and <code>WrappedString</code> is that calling transformer methods such as <code>filter</code> and <code>map</code> will yield a <code>String</code> object, whereas a <code>WrappedString</code> will remain a <code>WrappedString</code>.</p> </blockquote> <p>Both derive from <code>collection.GenSeqLike</code> which defines an equals method:</p> <pre><code>override def equals(that: Any): Boolean = that match { case that: GenSeq[_] => (that canEqual this) && (this sameElements that) case _ => false } </code></pre> <p>Both implement the <code>canEqual</code> (derived from <code>collection.IterableLike</code>) which <a href="https://github.com/scala/scala/blob/v2.10.0-M4/src/library/scala/collection/IterableLike.scala#L292" rel="noreferrer">returns always true</a>. But <code>StringOps</code> is not a <code>collection.GenIterable</code>:</p> <pre><code>scala> st1 sameElements st2 <console>:13: error: type mismatch; found : scala.collection.immutable.StringOps required: scala.collection.GenIterable[?] st1 sameElements st2 ^ </code></pre> <p>Whereas <code>WrappedString</code> does:</p> <pre><code>scala> st2 sameElements st1 res13: Boolean = true </code></pre> <p>So it should obvious why the first case returns <code>true</code> and the other one <code>false</code>.</p> <p>But why do both exist? I'm not totally sure why it is designed this way, but I think that's because of the fact that a String is not a collection in Scala. When we do some operation on a String like <code>"abc" flatMap (_+"z")</code> we wanna get back another String even though it is not always possible as shown by <code>"abc" map (_+1)</code>. This is what <code>StringOps</code> does. But when we have some method <code>def x[A](s: Seq[A]) = s.getClass</code> how shall we call it with a String? In this case we need <code>WrappedString</code>:</p> <pre><code>scala> x("a") res9: Class[_ <: Seq[Char]] = class scala.collection.immutable.WrappedString </code></pre> <p>So, <code>StringOps</code> is more lightweight as <code>WrappedString</code>. It allows us to call some methods on plain old <code>java.lang.String</code> without doing too much overhead. In 2.10 <code>StringOps</code> extend <code>AnyVal</code>. This means it is a value class and its existence can be optimized by scalac (no runtime overhead any more by wrapping the String). In contrast <code>WrappedString</code> allows us to handle a String as a real collection - as an <code>IndexedSeq[Char]</code>.</p>

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