Question

In language like python and ruby to ask the language what index-related methods its string class supports (which methods’ names contain the word “index”) you can do

“”.methods.sort.grep /index/i

And in java

List results = new ArrayList();  
Method[] methods = String.class.getMethods();  
for (int i = 0; i < methods.length; i++) {  
    Method m = methods[i];  
    if (m.getName().toLowerCase().indexOf(“index”) != -1) {  
        results.add(m.getName());  
    }  
}  
String[] names = (String[]) results.toArray();  
Arrays.sort(names);  
return names;  

How would you do the same thing in Scala?

Answer 1

Curious that no one tried a more direct translation:

""
.getClass.getMethods.map(_.getName) // methods
.sorted                             // sort
.filter(_ matches "(?i).*index.*")  // grep /index/i

So, some random thoughts.

• The difference between “methods” and the hoops above is striking, but no one ever said reflection was Java’s strength.

• I’m hiding something about sorted above: it actually takes an implicit parameter of type Ordering. If I wanted to sort the methods themselves instead of their names, I’d have to provide it.

• A grep is actually a combination of filter and matches. It’s made a bit more complex because of Java’s decision to match whole strings even when ^ and $ are not specified. I think it would some sense to have a grep method on Regex, which took Traversable as parameters, but…

So, here’s what we could do about it:

implicit def toMethods(obj: AnyRef) = new { 
  def methods = obj.getClass.getMethods.map(_.getName)
}

implicit def toGrep[T <% Traversable[String]](coll: T) = new {
  def grep(pattern: String) = coll filter (pattern.r.findFirstIn(_) != None)
  def grep(pattern: String, flags: String) = {
    val regex = ("(?"+flags+")"+pattern).r
    coll filter (regex.findFirstIn(_) != None)
  }
}

And now this is possible:

"".methods.sorted grep ("index", "i")