Editing Function object (section)

== In Ruby ==
In [[Ruby (programming language)|Ruby]], several objects can be considered function objects, in particular Method and Proc objects. Ruby also has two kinds of objects that can be thought of as semi-function objects: UnboundMethod and block. UnboundMethods must first be bound to an object (thus becoming a Method) before they can be used as a function object. Blocks can be called like function objects, but to be used in any other capacity as an object (e.g. passed as an argument) they must first be converted to a Proc. More recently, symbols (accessed via the literal unary indicator <code>:</code>) can also be converted to <code>Proc</code>s. Using Ruby's unary <code>&</code> operator&mdash;equivalent to calling <code>to_proc</code> on an object, and [[duck typing|assuming that method exists]]&mdash;the [[Ruby Extensions Project]] [https://web.archive.org/web/20060425104650/http://blogs.pragprog.com/cgi-bin/pragdave.cgi/Tech/Ruby/ToProc.rdoc created a simple hack.]

<syntaxhighlight lang="ruby">
class Symbol
  def to_proc
    proc { |obj, *args| obj.send(self, *args) }
  end
end
</syntaxhighlight>

Now, method <code>foo</code> can be a function object, i.e. a <code>Proc</code>, via <code>&:foo</code> and used via <code>takes_a_functor(&:foo)</code>. <code>Symbol.to_proc</code> was officially added to Ruby on June 11, 2006, during RubyKaigi2006. [https://web.archive.org/web/20060820025032/http://redhanded.hobix.com/cult/symbolTo_procExonerated.html]

Because of the variety of forms, the term Functor is not generally used in Ruby to mean a Function object.
Just a type of dispatch [[delegation (programming)|delegation]] introduced by the [https://web.archive.org/web/20070107205748/http://facets.rubyforge.org/ Ruby Facets] project is named as Functor. The most basic definition of which is:

<syntaxhighlight lang="ruby">
class Functor
  def initialize(&func)
    @func = func
  end
  def method_missing(op, *args, &blk)
    @func.call(op, *args, &blk)
  end
end
</syntaxhighlight>

This usage is more akin to that used by functional programming languages, like [[ML (programming language)|ML]], and the original mathematical terminology.