glennj's github pages

learnin'

Project maintained by glennj Hosted on GitHub Pages — Theme by mattgraham

Pharo

Pharo is a Smalltalk dialect. In my university days, Smalltalk was the OO teaching language, so it has a fond place in my heart.

I won’t dig into it. See the Pharo website to learn more.

Extension methods

Because Pharo is typically coded within the Pharo UI, the entire language is available to you for browsing but also modifying! You can easily add new methods to any class. But that can quickly lead to a real mess.

Pharo has projects to act as namespaces for your code. When you add new methods to existing classes, they can be configured as extension methods, stored in the context of your project.

Let’s walk through an example, starting with the Armstrong Numbers exercise. That exercise gets you to write an ArmstrongNumbers class, and an isArmstrongNumber: anInteger instance method. Suppose we want to be able to provide isArmstrong as an instance method on the Integer class. (Note this is in a Pharo 12 image).

  1. first, let’s just try it in the Playground

    integer doesn't understand isArmstrong message

  2. in the Browser, navigate to Kernel -> Numbers -> Integer; select the “+ Inst. side meth” tab.

    create an instance method for Integer

  3. type in the method implementation and save (cmd-S on the mac); we’ve created an Integer instance method.

    newly created instance method

  4. select the “extension” checkbox in the bottom-right corner; select the Exercise@ArmstrongNumbers package to store it in; click OK.

    choosing the package to store the extension method

  5. now the method name is grey in the instance method list, and the package name shows up at the bottom of the browser.

    it's now an extension

  6. and if we navigate back to the Exercise@ArmstrongNumbers package, we can see “Integer” show up in the class list (grey) where we can find our extension method. And it’s only now that I realize I’ve mistyped it – not gonna redo the screenshots.

    the view from the Exercise package

So now, back to the playground and try it again: