Proposed Spec for Eiffel Introspection Library (v0.1.1 - 3/28/99)

Introduction

This page describes a proposed specifications for Eiffel introspection library. Introspection is also known as reflection, meta-level programming or meta-object protocols.

An introspection library allows a running program to examine the structure of its objects. The minimal number of tasks such a library must perform is:

• Object manipulations
  • Create Eiffel objects given the type name as a string.
  • Call a routine on an object given the routine name as a string.
  • Traverse all the attributes of an arbitrary object and extract or set the values of its attributes.
• Type manipulation
  • Given an Eiffel class determine its direct parents.
  • Given two Eiffel classes determine if their types conform.
  • Determine if a type of an object conforms to a given class.

The library must be powerful enough to to implement the ELKS class STORABLE entirely in Eiffel.

Requirements

There are several somewhat arbitrary levels of implementation that would make this library useful. They are:

• Level 1

  Allow manipulation of attributes (setting and reading) and creation of objects given EIFFEL_TYPE. Ability to disable and enable assertion checking. Example application: STORABLE.

• Level 2

  In addition to level 1 calling of routines is possible. Example application: Remote Eiffel Invocation, CORBA interface.

• Level3

  The ability to examine the state of assertions at runtime. Example application: debugger (?).

• Level 4

  Ability to examine compiled, but not running systems. Example application: case tools.

Proposed Classes

• EIFFEL_SYSTEM - contains some global information about the system and acts as a factory class for instances of EIFFEL_TYPE. It is possible that not all objects in a running Eiffel system will have an corresponding EIFFEL_TYPE instance to allow compiler optimizations.
• EIFFEL_TYPE - describes an Eiffel type. Allows creation of instances of the type and invocation of procedures and functions. Also allows manpulations of attributes.
• EIFFEL_FEATURE - abstract description of an Eiffel feature.
• EIFFEL_ROUTINE - description of a routine, including pre- and postconditions, and argument types.
• EIFFEL_FUNCTION - description of a function and its return type.
• EIFFEL_PROCEDURE - description of a procedure.
• EIFFEL_ATTRIBUTE - description of an attribute.
• EIFFEL_ASSERTION - description of an assertion.
• EIFFEL_PARAMETER - description of a routine parameter.

Inheritance

EIFFEL_FEATURE
	EIFFEL_ATTRIBUTE
	EIFFEL_ROUTINE
		EIFFEL_FUNCTION
		EIFFEL_PROCEDURE

Implementation Notes

Today it is possible to implement such library at Level 1 with ISE's compiler. Level 2 maybe possible with the "delayed calls" features, but I haven't looked into it.

Changelog

• 3/28/99 - changed EIFFEL_CLASS to EIFFEL_TYPE. Made EIFFEL_TYPE match TYPE as defined by the ISE Agent paper. Many fixes suggested by many people.

References

• Smalltalk-80 - Goldberg, Robson
• The Art of Meta-Object Protocol - Kiczales, Rivieres, Bobrow
• Agents, iteration and introspection - Bertrand Meyer

Contributors

These classes and ideas are based on work and discussions with Jean-Pierre Sarkis, Philippe Stephan, Gurvan Lullien and Nick Leaton.

The comments of the following people were important in the improvement of this document: Bertrand Meyer, Eric Bezault, Alexander Kogtenkov, and Sergei S. Ivanov.

I'm sorry if I left anyone out of this list - I got a lot of emails following the initial positing.