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Routines should be properly equipped with pre- and postconditions and classes with invariants. This is useful as documentation in addition to the header comments to make sure that the routines and class instances are correctly used. These assertions can also be enabled when running the test suite in $GOBO/library/<library-name>/test in order to check the correctness of the library classes.

All assertions should have a tag, as in the following example:

_   foo_not_void: foo /= Void

Note that in the example above the tag “foo_not_void” is preferred to “foo_exists” as it may cause confusion when exists is a feature of the class of foo. So using systematically “*_not_void” is a good way to avoid such possible confusion.

Note Clause

Each class should have a note clause at the top of the file which looks like that:


_   description:

_   _   "Short description of the class"

_   library:    "Gobo Eiffel Lexical Library"
_   copyright:  "Copyright (c) 2000-2016, Eric Bezault and others"
_   license:    "MIT License"
_   date:       "$Date$"
_   revision:   "$Revision$"

Put a short description of the class in the “description” field. Replace “Lexical” in the “library” field by the name of your library. Replace “Eric Bezault” by your name in the “copyright” field. The fields “date” and “revision” are automatically expanded by the Version Control Systems supporting these keyword expansions. Note that Git does not support such expansion.

Header Comments

Every feature and feature clause should have a header comment such as:

feature -- Access

_   title: STRING
_   _   _   -- Title displayed in the title bar

feature -- Setting

_   set_title (a_title: like title)
_   _   _   -- Set `title' to `a_title'.
_   _   require
_   _   _   a_title_not_void: a_title /= Void
_   _   do
_   _   _   title := a_title
_   _   ensure
_   _   _   title_set: title = a_title
_   _   end

(Borrow guidelines to write good header comments from OOSC2 section 26.4 page 886-888.)

Free Comments

They should give useful information and not just paraphrase the software text. They should appear on the line before the instruction(s) to be explained and should have one more indentation level to the right than the instruction(s).


Semicolons are optional in Eiffel. For consistency reason, they should not be used in the Gobo Eiffel classes. The only places where they are used are:


Exceptions should only be raised when an unexpected behavior occurs. Reading an integer from the standard input when the user actually typed “hello”, or trying to open a file in read mode when the file does not exist (it could just have been deleted) are not considered as unexpected behaviors in my point of view.

Also raising exceptions in the creation routine should be avoided since it is not clear to me what should happen in that particular case. It is preferred to properly create the objects and then call the routines which may raise the exception.

Routines which may raise exceptions should make it clear in their header comment. (There is no need to report the fact that a No_more_memory exception can be raised in each routine creating objects though ;-))

Copyright 2001-2016, Eric Bezault
Last Updated: 22 December 20016