Ruby Language Dynamic Evaluation Dynamically Creating Methods from Strings
Example
Ruby offers define_method as a private method on modules and classes for defining new instance methods. However, the 'body' of the method must be a Proc or another existing method.
One way to create a method from raw string data is to use eval to create a Proc from the code:
xml = <<ENDXML
<methods>
<method name="go">puts "I'm going!"</method>
<method name="stop">7*6</method>
</methods>
ENDXML
class Foo
def self.add_method(name,code)
body = eval( "Proc.new{ #{code} }" )
define_method(name,body)
end
end
require 'nokogiri' # gem install nokogiri
doc = Nokogiri.XML(xml)
doc.xpath('//method').each do |meth|
Foo.add_method( meth['name'], meth.text )
end
f = Foo.new
p Foo.instance_methods(false) #=> [:go, :stop]
p f.public_methods(false) #=> [:go, :stop]
f.go #=> "I'm going!"
p f.stop #=> 42
