dynamic method look-up?

From: Eijiro Sumii (sumii@lute.is.s.u-tokyo.ac.jp)
Date: Thu Apr 02 1998 - 12:49:36 MET DST

Message-Id: <199804021049.TAA20435@lute.is.s.u-tokyo.ac.jp>
To: caml-list@inria.fr
Subject: dynamic method look-up?
Date: Thu, 02 Apr 1998 19:49:36 +0900
From: Eijiro Sumii <sumii@lute.is.s.u-tokyo.ac.jp>

Hello, everyone. I'm sorry that I don't write French version. I know
very little about French language. (Though I'm not very good at
English, either.)

I have a question about the implementation of method invocation in
ocaml. Whenever I compile a tiny program like the following one by
ocamlopt with `-S' option (on any platform),

    let invoke_foo obj = obj # foo;;
    class c1 () =
      method foo = 123
    class c2 () =
      method foo = 456
      method bar = "abc"
    let o1 = new c1 ();;
    let o2 = new c2 ();;
    print_int ((invoke_foo o1) + (invoke_foo o2));;
    print_newline ();;

the assembly code generated by ocamlopt seems to contain an ascii
string "foo" and to use it at runtime. Is the method `foo'
dynamically looked up before its invocation? If it is, isn't there a
more efficient way than dynamic method look-up to implement method
invocation? (something like index passing in Ohori's polymorphic
record calculus [1], or implicitly generating and passing some
fuctions like a coercion function and a put function in Hofmann &
Pierce's positive subtyping [2])

// Eijiro Sumii <sumii@yl.is.s.u-tokyo.ac.jp>
// Kobayashi Laboratory, Department of Information Science,
// Faculty of Science, University of Tokyo

[1] Atsushi Ohori. A polymorphic record calculus and its
compilation. ACM Transactions on Programming Languages and Systems,
Vol 17, No 6, Pages 844-895.

[2] @inproceedings (HofmannPierce94a,
author = "Martin Hofmann and Benjamin Pierce" ,
title = "Positive Subtyping",
booktitle = "Proceedings of Twenty-Second Annual ACM Symposium on
                  Principles of Programming Languages",
year = "1995" ,
month = jan,
publisher = "ACM" ,
pages = "186--197",
note = "Full version in {\em Information and Computation},
                  volume 126, number 1, April 1996.
                  Also available as University of Edinburgh technical
                  report ECS-LFCS-94-303, September 1994."

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