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POReferring to a Enumeration Value type in a method signature
 

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    <p>I would like to add a method to scala.Enumeration. My first approach was to try to extend it, but was bitten by <a href="https://stackoverflow.com/questions/1938309/how-to-add-a-method-to-a-scala-enumeration-object">this</a>. My second approach was to try to define a method, and pass in the Enumeration - if that worked, I hoped to use an implicit conversion. I'm having a hard time preserving type with the return type of the method, however.</p> <pre><code>object EnumExample { object SampleEnum extends Enumeration { val include, exclude = Value } def parse[T &lt;: Enumeration](name:String, enum:T):T#Value = enum.valueOf(name) match { case Some(x) =&gt; x case x =&gt; throw new RuntimeException("No field named '" + name + "' found on enum " + enum + ", legal values = " + enum.values) } def main(args:Array[String]) = { //compiles fine, and preserves custom type val withNameExample:SampleEnum.Value = SampleEnum.withName("include") //also fine, but we lost type info val enumWithHash:Enumeration#Value = parse("include", SampleEnum) /** error: type mismatch; found : Main.$anon.EnumExample.SampleEnum#Value required: Main.$anon.EnumExample.SampleEnum.Value val parseExample:SampleEnum.Value = parse("include", SampleEnum) * */ val customTypeWithHash:SampleEnum.type#Value = parse("include", SampleEnum) //same error val customTypeWithDot:SampleEnum.Value = parse("include", SampleEnum) } } </code></pre> <p>One obvious fix would be to just remove the return type declaration from the parse method, but that gives me a "illegal dependent method type". This leaves me with lots of questions:</p> <ol> <li><p>Is this possible to specify? One way or another, I'd like to get a nice error message when parsing an enumeration field in from a String.</p></li> <li><p>Why do I get the "illegal dependent method type"?</p></li> <li><p>What precisely is the "#" operator(?) in this case?</p></li> </ol>
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    1. USAdam Rabung
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    1. COCame across this question, tried it but I have compilation error in `enum.valueOf(name) match {` saying that "value valueOf is not a member of type parameter T". So why is that so? I use scala 2.9.1.
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    2. COI think they removed valueOf in 2.9 - use withName instead. Better yet , I'd recommend sealed traits/case objects as described here: http://stackoverflow.com/questions/4236251/should-i-prefer-sealed-class-or-enumeration-in-scala. This approach has its own warts, but in my experience it's more useful.
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      1. USAdam Rabung
 

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