A flexible interface for any class would be when

For example:
 All parameters and parameter names are put in an array.
  a=array('Username'->'peter','password'->'mypassword','e_mail'->'peter@nowhere.com');

An object is initialized like.
  user.init(a)

The idea is that any object can be initialized by the same function init() with an array a as atribute.

''(this is a draft page) please add some ideas, fix my poor english''

----

Python functions often do this.  The ''keyword arguments'' may also be mixed with ''normal'' arguments and default values for the ''normal'' arguments, e.g.:

  >>> def foo(first=True, **kwargs):
  ...     print "%s, %s" % (str(first), str(kwargs))
  ...
  >>> foo()
  True, {}
  >>> foo(False)
  False, {}
  >>> foo(foo=1)
  True, {'foo': 1}
  >>> foo(foo=1, bar=2)
  True, {'foo': 1, 'bar': 2}
  >>> foo(False, foo=1, bar=2)
  False, {'foo': 1, 'bar': 2}

The ''kwargs'' name refers to a dictionary, and dictionaries support default values for non-existent keys.  This makes it possible to write code like:

  def foo(**kwargs):
      name = kwargs.get('name', "Default User")
      ...

This is a relatively clean way of writing semi-polymorphic functions that support an arbitrary number of key=value pairs.