From: Greg McIntyre <greg@...>
Date: 2003-11-21T09:37:16+09:00
Subject: Re: New Type Checking System Idea

I like your idea, Sean, but it's too much effort! If it is onerous then
it won't be used. Perhaps if we based it upon method name and arity
(essentially replacing a bunch of respond_to?() calls with arity
checks added in as a bonus). This is because it requires no extra effort
on the programmer's part, so it fits into the existing Ruby syntax.

I took your code and rewrote it a bit...


class IO
  class Stream
    def eof?
      # ...
    end
  end

  # Class IO::Stream defined. Interface IO::Stream defined:
  # [[eof?,0]]

  class InputStream < IO::Stream
    def read(maxbytes)
      # ...
    end
  end

  # Class IO::InputStream defined. Interface IO::InputStream
  # defined: [[eof?,0], [read,1]]
end 

# Class IO defined. Interface IO defined: []


### Example of class definition using an interface

class Stdin
  implements IO::InputStream

  # Interface: []
  # Needed: [[eof?,0], [read,1]]

  def eof?
    # ...
  end

  # Interface: [[eof?,0]]
  # Needed: [[eof?,0], [read,1]]

  def read(maxbytes)
    # ...
  end

  # Interface: [[eof?,0], [read,1]]
  # Needed: [[eof?,0], [read,1]]

  def someothermethod
  end

  # Interface: [[eof?,0], [read,1], [someothermethod,0]]
  # Needed: [[eof?,0], [read,1]]

end # RUN-TIME CHECK: Promises fulfilled. Interface Stdin produced.


### Example of re-implementing class methods

class Stdin
  def read(maxbytes=20)
    # do something different
  end

  # Interface: [[eof?,0], [read,-1], [someothermethod,0]]
  # Needed: [[eof?,0], [read,1]]

end # RUN-TIME CHECK: Promises fulfilled. Interface Stdin kept.
    # => Warning, default value for maxbytes in method read may
    #    never be used by interface(?)
    # => No warning, interface made more general(?)


### Example of breaking class interface

class Stdin
  def read(maxbytes, retries)
    # do something different
  end

  # Interface: [[eof?,0], [read,2], [someothermethod,0]]
  # Needed: [[eof?,0], [read,1]]
  
end # RUN-TIME CHECK: Promises broken. Interface Stdin deleted.
    # => Raise type error(?)


### Example of re-implementing object methods

class << $stdin
  def read(maxbytes)
    # do something different again
  end

  # Interface: [[eof?,0], [read,1], [someothermethod,0]]
  # Needed: [[eof?,0], [read,1]]

end # RUN-TIME CHECK: Interface fulfilled. No action taken.


-- 
Greg McIntyre ======[ greg@puyo.cjb.net ]===[ http://puyo.cjb.net ]===