signature

Scala: A look at flatMap and map on Option

As a quick Scala tip, if you haven’t worked with the flatMap on an Option much, it can help to know that flatMap’s function should return an Option, which you can see in this REPL example:

scala> Some(1).flatMap{ i => Option(i) }
res0: Option[Int] = Some(1)

You can tell this by looking at the function signature in the scaladoc for the flatMap method on the Option class:

This is a page from my book, Functional Programming, Simplified

Pure Function Signatures Tell All

“In Haskell, a function’s type declaration tells you a whole lot about the function, due to the very strong type system.”

Learn You a Haskell for Great Good!

One thing you’ll find in FP is that the signatures of pure functions tell you a lot about what those functions do. In fact, it turns out that the signatures of functions in FP applications are much more important than they are in OOP applications. As you’ll see in this lesson:

Android AsyncTask - Using "Void, Void, Void" parameters (code signature)

As a quick note to self, this is how I just created an Android AsyncTask with “Void, Void, Void” parameters:

private class DeleteImagesTask extends AsyncTask<Void, Void, Void> {
    @Override
    protected Void doInBackground(Void... params) {
        deleteSelectedGalleryItems();
        return null;
    }
    @Override
    protected void onPostExecute(Void param) {
        cleanupUiAfterCancelOrDelete();
        galleryItemAdapter.notifyDataSetChanged();
    }
}

Show the method signature with control-space keystroke

Using Eclipse, if your cursor is positioned in between the parentheses of a method call, the [Control][Spacebar] keystroke will show you the signature of the method, i.e., the parameters that the method accepts. I just read where the documentation shows that you should use the [Control][Shift][Spacebar] keystroke to see method parameters, but I've found that [Control][Spacebar] works fine for me.