一直对动态语言的的method obj和function obj感到困惑：
今天看了一个较好的区分介绍:
A function is a piece of code that is called by name. It can be passed data to operate on (ie. the parameters) and can optionally return data (the return value).
All data that is passed to a function is explicitly passed.
A method is a piece of code that is called by name that is associated with an object. In most respects it is identical to a function except for two key differences.
- It is implicitly passed the object for which it was called
- It is able to operate on data that is contained within the class (remembering that an object is an instance of a class - the class is the definition, the object is an instance of that data)