return type decorator.rb

[1] pry(main)> def returns(type)
[1] pry(main)*   ->(method_name) {   
[1] pry(main)*     old_method = instance_method(method_name)    
[1] pry(main)*     define_method(method_name) do |*args, &block|    
[1] pry(main)*       return_value = old_method.bind(self).call(*args, &block)      
[1] pry(main)*       unless return_value.class <= type      
[1] pry(main)*         raise TypeError, "Return value is not of type #{type}!"        
[1] pry(main)*       end        
[1] pry(main)*       return_value      
[1] pry(main)*     end      
[1] pry(main)*   }
[1] pry(main)* end  
=> :returns
[2] pry(main)> class Hello
[2] pry(main)*   returns(Integer).call def hello
[2] pry(main)*     5
[2] pry(main)*   end  
[2] pry(main)*   
[2] pry(main)*   returns(String).call def goodbye
[2] pry(main)*     5
[2] pry(main)*   end  
[2] pry(main)* end  
=> :goodbye
[3] pry(main)> Hello.new.hello
=> 5
[4] pry(main)> Hello.new.goodbye
TypeError: Return value is not of type String!
from (pry):7:in `block (2 levels) in returns'
[5] pry(main)>