Last weekend,
zan showed me howto use parsetree & ruby2ruby to dynamically extract a method definition in plain ruby code:
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| %w{rubygems ruby2ruby parse_tree}.each {|lib| require lib }
class Hello
def self.hello
puts "class says hello"
end
def hello
puts "instance says hello"
end
end
extract_code = lambda do |klass, method|
sexp = ParseTree.translate(klass, method)
Ruby2Ruby.new.process(Unifier.new.process(sexp))
end
instance_method_code = extract_code[Hello, :hello]
puts instance_method_code
# >> def hello ; puts("instance says hello") ; end
|
To get the class method:
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| metaclass = (class << Hello ; self ; end)
class_method_code = extract_code[metaclass, :hello]
puts class_method_code
# >> def hello ; puts("class says hello") ; end
|
It is even possible to extract the entire class definitions:
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| puts extract_code[World, nil]
# >> class World < Object
# >> def hello ; puts("instance says hello") ; end
# >> def self.hello ; puts("class says hello") ; end
# >> end
|
There are probably tonnes of code stuff you can do with the above capability. One immediate use case i can think of is appending new instance/class methods to another class:
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| class World ; end
World.class_eval instance_method_code
World.instance_eval class_method_code
World.hello # yields: class says hello
World.new.hello # yields: instance says hello
|
Another is that we can store the method definition somewhere (db, file, ...), redefine, distort, assault, murder, arson the existing class, and later just rollback the damages:
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| cache = {'Hello.hello' => extract_code[Hello, :hello]}
File.open('/tmp/original_methods', 'w') {|f| Marshal.dump(cache, f) }
class Hello
def hello ; puts "instance is murdered" ; end
end
puts Hello.new.hello
# >> instance is murdered
# Do lots of other bad stuff, and to undo the damages:
cache = File.open('/tmp/original_methods', 'r') {|f| Marshal.load(f) }
Hello.class_eval = cache['Hello.hello']
puts Hello.new.hello
# >> instance says hello
|
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