From: Christian Szegedy <szegedy@...>
Date: 2001-05-15T22:26:59+09:00
Subject: [ruby-talk:15160] Re: Discussion on new Ruby features

Sorry, I don't know how to reply to this list,
so my replay will probably create a new thread.

Michael Neumann wrote:
> or perhaps with additional range checking: 
> 
> def addInteger(a :< Fixnum, b > 0 : Fixnum) 
> end

I don't understand the syntax of the first parameter, but generally,
I support your idea. Additional constraint would also enhance 
optimization possibilities.

> Of course sometimes it would be nice to check for types this way,
> but it's not often enough used, I guess.
>
> For that you could befine a method "must" in Object (like the one
> in amstd), which can be used this way:
>
>  a.must Fixnum
>  And raises an exception if the type is not equal.

I find the it less readable, and less suggestive and less effective
(in terms of possible runtime, assuming optimal implementation of
the above feature). To effectiveness: consider the following piece
of code:

  def f(x : X)
  end

  def g(x : X)
     f(x)
  end

A good compiler would easily eliminate the second check, but also
a single check could be more effectively performed than now.

> The problem is that classes in Ruby are just objects, i.e. they are
> dynamic. They have no static signature to check for. 

I think of a signature which is automatically generated 
and can be checked faster on need. The main concern here is not just 
readability, but speed. I could also imagine some check-caching
approach: generic tests for classes could be cached and invalidated
on extension of the class. 

In fact, adding such constraints to code has both advantages and 
disadvantages:

Advantage:    Optimizability, nicer syntax, better checking at parse time.
Disadvantage: Non-generity (i.e. it makes your code less generic =>
less extendable)
It depends on the situation, which one is more important.
I think: we need both.

> What you could do is define an interface definition, and check if the
> object "implements" this interface.
> But this could be done in pure Ruby, I think.

I agree. Ruby is easy to write, extremely extandable. BUT: hard to optimize.
Of course, extandability is an important issue and we should not give it up
or even reduce it.

I think that the current freeze machanism, and perhaps an optional  more 
agressive one, which does not allow unfreeze at all, e.g something like that:

   frozen class X
      ... 
   end

would also be an interesting feature, worth considering and could be
essential for the usability of such features.

For a Ruby code compiled to C, one could consider different scenarios:

1) Shared object: This one is the most extendible, and therefore the
   one which is the hardest to optimize. Even in this case, a reasonable 
	hiding strategy would expand the optimization possibilities.

2) Stand-alone-object which allows evaluates scripts from files or strings.
   Roughly the same situation as in 1)

3) Stand-alone-object which does not interprete anything:
   Much more optimizable than 1) or 2) since a compiler can have all
   information about the structure of the program (no possible extensions).
	Disadvantage: unsuitable for large projects, bacause of probable slow
   compilation time.

I could imagine the following mechanism:
   An own object/library file format which contains the following section:

1)	(assembler) compiled code for the private parts of the code (as a normal
	            object file).

2)	 bytecode for the exported parts: for faster linkage

3)  information on external extensions: i.e. a decription on how far this
    unit tries to extend other units. It would be helpful for optimizing
    other units.

Ruby would have its own linker:
    Using section 3) determines how far the byte-code objects could be 
    extended by other units and optimizes/compiles them.
	 After that it could call the standard linker.

This thoughts are of course very vague, but perhaps a starting point
worth consideration.

best regards, Christian