inspired by some lisp magic of runtime edit sourcecode,
I want to do it in ruby. looks like I cannot get sourcecode from method/class, is there a way to do it?
I write a sample sourcecode here:
def helloworld n
"hello #{n}"
end
o = Kernel.method :helloword
Kernel.define_singleton_method o.name do |n|
eval o.source_code.sub('hello', 'hello world')
end
helloworld 'halida' #=> 'hello world halida'
You can easily get source code for a method in Ruby.
Imagine the following hypothetical class:
class Klass
def self.foo
:foo
end
def bar
:bar
end
end
As you can see, this class has two methods:
Use .method and .instance_method to access them programmatically:
m1 = Klass.method :foo
=> #<Method: Klass.foo>
m2 = Klass.instance_method :bar
=> #<UnboundMethod: Klass#bar>
You can use the .source method to view their source code:
puts m1.source
def self.foo
:foo
end
=> nil
puts m2.source
def self.bar
:bar
end
=> nil
Because Ruby has open classes and dynamic loading, you can also add or change methods at run time. Just re-open the class and redefine the method:
Klass.foo
=> :foo
class Klass
def self.foo
:foobar
end
end
Klass.foo
=> :footer
The other methods previously defined in the class will remain unaffected:
Klass.bar
=> :bar
WARNING: Redefining class behavior during runtime (also called "Monkey Patching") is a very powerful tool, it can also be somewhat dangerous. Current versions of Ruby support a much more controlled way of going about this called 'refinements'.
You can't get the string representation of a part of the code, edit it and expect Ruby to reevaluate your changes. The only way to do something near to what you want is using ParseTree to get s-expressions of the source, edit and use Ruby2Ruby to generate a string of ruby code. Them add def ... and end to the string and call eval with it.
It's too hard and error-prone to be useful in a real-world situation. But I don't know any other way.
Note: ParseTree only works on Ruby 1.8.
.method.source for class methods or .instance_method.source for instance methods. If you want to edit the string and reapply it you can just open the class redefine the method and use eval on the new string.class_eval and instance_evalHave a look at method_source gem. It's used by pry REPL for show-method command.
Looks like this gem utilizes standard Method#source_location (available in Ruby 1.9) to locate method and get its source code. Obviously, it doesn't work for dynamically defined methods and C methods. See docs for more information.
