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Defining methods with double greater than sign (>>) in Smalltalk

In the book Smalltalk Best Practice Patterns from Kent Beck, the double greater sign (>>) is used to define methods like this:

Point class>>x: xNumber y: yNumber
    ^self new
        setX: xNumber
        y: yNumber

Point>>setX: xNumber y: yNumber
    x := xNumber.
    y := yNumber.
    ^self

However, I cannot get it run in GNU Smalltalk.

Is it valid syntax in some implementation of Smalltalk? Or is it just kind of pseudo code?

Solution

  • In fact this is Pseudo code.

    In other languages you would use the . to tell people that the method is in this class but in smalltalk you write >>

    What you would do in a Smalltalk like Squeak or Pharo for

    Point class>>x: xNumber y: yNumber
    ^self new
        setX: xNumber
        y: yNumber
    1. Open the System Browser
    2. klick on class, a button that will show you the class side of the class.

    3. paste the method in the text area with the source code:

      x: xNumber y: yNumber
    ^self new
        setX: xNumber
        y: yNumber

    4. Strg-s to save the code

    For 

    Point>>setX: xNumber y: yNumber
    x := xNumber.
    y := yNumber.
    ^self

    You would do the same but not use the class side