Quickfix to Expand Case-Class Bindings in Pattern Matching

When writing Scala code that involves pattern matching I often work with (nested) case classes and sequences of case classes. I usually start with a simple binding like this

case class Person(firstName: String, lastName: String)

List(Person("Mirko", "Stocker")) match {
  case person :: Nil =>; ...

and then when I need to access members of the matched class convert it to use the extractor:

List(Person("Mirko", "Stocker")) match {
  case Person(firstName, lastName) :: Nil => ...

What’s tedious about that step is that one needs to know how many arguments there are and name all the bindings. But not for much longer! I wrote a quick-fix for the Scala IDE that does this for you:

Ctrl+1 brings up the available quick fixes:

And this is what happens when the binding you’re expanding is used in the pattern’s body:

It also works if you use a typed pattern where the type is a case class:

This feature isn’t in the recently released Milestone 1, but it should be part of the next one (or one of the upcoming nightly builds). Suggestions for a better wording – expand case class binding – are welcome 🙂


Move Class, Object and Trait Refactoring for Scala

After lots of bug fixing and improvements of existing refactorings in the Scala IDE, I took a few days off between Christmas and New Year to finally implement a completely new refactoring: Move Class.

Move Class (see Fowler’s description if you’re unfamiliar with it) moves a top-level Class, Object or Trait definition into a different package. And if there exists more than one declaration in the file, you can choose to split-off one of the declarations or to move them all. The refactoring will move all the necessary imports along, and also update all the references to the moved implementation (other imports, or qualified names) in the project.

The refactoring can either be invoked from the menu, or by drag-and-dropping a file in the Package Explorer. Here are some screenshots of the refactoring in action:

It’s also possible to create a new package during the refactoring:

As usual, the changes can be previewed. In this case, the class is removed from the original source file and an import is added to its new location:

Looking at the created file, we see the changed package declaration (a copyright notice in the original file would also have been copied along to the new file) and some imports to types of the originating package:

There are a few limitations: the refactoring works only on Scala code, and it simply ignores visibility issues, so moving might result in compilation errors (cursory tests showed that this also happens in Eclipse JDT — my gold standard for refactoring implementations).

The Move refactoring will be part of the 2.1 release of the Scala IDE, for which there are nightly builds available.

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Organizing Imports in Scala

Organize Imports was a very often requested feature for the Scala IDE for Eclipse, so I wrote the first very limited version as part of my thesis. It couldn’t do much more than sorting the imports and collapsing them from multiple import statements to a single one. At the beginning of this year, Daniel Ratiu provided a patch that made Organize Imports recognize some of the unused imports.

One limitation we still had was that we didn’t really know the complete set of required imports, but this is required to, for example, replace all wildcard imports with the actually used ones. Another request was that it should be possible to push import statements down to the scope where they are used. For this, we also need to know which parts of the code require which imports.

Yet another motivation to write some code to analyze dependencies was that I want to provide a move refactoring, and for this too we need to know some of the dependencies in the code. But that’s for a future post, back to what we have now:

As you can see, just like the JDT, we can now configure grouping for imports (groups are separated by a blank line), and it’s possible to expand or collapse imports from the same package. The Scalaz or Lift users will likely want to always use wildcard imports on some packages and types, so this is also possible. The JDT has some additional options, but I think I implemented the important ones.

And there’s more! No, not Reversi, but if there are missing imports in the file, Organize Imports will add them for you:

This all is part of the latest beta release of the Scala IDE, so please give it a try and open a ticket if you find a problem.

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