Chatter - Smalltalk Wannabe for Ruby¶ ↑

This is a library that allows you to define a “multi-named” method, like Smalltalk.

Example¶ ↑

require 'chatter'

class Kid
  def initialize(name)
    @name = name
  end

  extend Chatter

  # this is how to use "chat" to define a multi-named method
  chat(:pass, :to, :saying) do |item, target, words|
    puts "#{@name} passes #{item} to #{target}, saying '#{words}'"
  end
end

jack = Kid.new('Jack')

# this is how the method is called
jack.pass('ball').to('Jill').saying('catch!')
# >> "Jack passes ball to Jill, saying 'catch!'"

Motivation¶ ↑

This library is mostly tailored for creating DSLs. For example, a DSL for describing finite-state machines can look like

a_state - a_symbol > another_state

And with Chatter this can be easily implemented with

class State
  chat(:-, :>) {|symbol, target_state| ...}
end

For another example, (this code does not work yet due to the first limitation listed below) a Ruby API for a GUI tookit might use Rubyish accessor methods (property, property=) as aliases to (getProperty, setProperty). But this is not directly possible with properties that take arguments, for example, TableWidget#getCellText(x, y), TableWidget#setCellText(x, y). By using

class TableWidget
  chat(:cell_text, :[]) do |_, (x, y)|
    getCellText(x, y)
  end

  chat(:cell_text, :[]=) do |_, (x, y, value)|
    setCellText(x, y, value)
  end
end

We can do

a_table_widget.cell_text[x, y] += " (cool)"

Limitations¶ ↑

• “Multi-name methods” with overlapping components are not yet supported. For example, if you do

  chat(:pass, :to) {}
  chat(:pass) {}
  

  Only the second one will work.

• Sub-methods that take blocks are not yet supported. For example, you cannot yet implement

  (1 == 1).ifFalse {'wrong'}.ifTrue {'right'}
  

• Sub-methods must be called in order they’re listed in chat