How do I add a method to an object instance with a variable from the current scope (Ruby)?

This is hard to explain as a question but here is a code fragment:

n = "Bob"
class A
end
def 开发者_运维技巧A.greet
  puts "Hello #{n}"
end
A.greet

This piece of code does not work because n is only evaluated inside A.greet when it is called, rather than when I add the method.

Is there a way to pass the value of a local variable into A.greet?

What about if n was a function?

Use metaprogramming, specifically the define_singleton_method method. This allows you to use a block to define the method and so captures the current variables.

n = "Bob"

class A
end

A.define_singleton_method(:greet) do
  puts "Hello #{n}"
end

A.greet

You can use a global ($n = "Bob")...

Although I prefer Nemo157's way you can also do this:

n = "Bob"

class A
end

#Class.instance_eval "method"
A.instance_eval "def greet; puts 'Hello #{n}' end"

#eval Class.method
eval "def A.greet2; puts 'Hi #{n}' end"

A.greet
A.greet2