Boost.Assertion

From: williamkempf_at_[hidden]
Date: 2001-04-16 15:39:34

I've been researching the web for articles on DbC with C++ to come up 
with ideas for Boost.Assertion.  This is what I've found and comments 
I have on each site:

http://www.cs.unc.edu/~smithja/MIMS/DataModel/research/DBC.html

A general discussion about DbC with references to implementation 
languages and tools.  If you're unfamiliar with DbC this is a good 
place to start.

http://www-und.ida.liu.se/~freku045/dbcpp/

This is a pre-processing approach to adding DbC to C++.  This 
probably won't be of much help when designing an assertions library 
but is worth looking at any way.

http://www.halcyon.com/www3/jesjones/Whisper/Description.html

This is a complete C++ GUI framework with the only interesting part 
for this discussion being three macros, PRECONDITION, POSTCONDITION 
and CHECK_INVARIANT.  The page makes this sound like pretty much what 
I'm trying to do with Boost.Assertion but I've not looked into the 
code to evaluate it yet.

http://www.cbuildermag.com/features/2000/08/cb200008gm_f/cb200008gm_f.
asp

Talks about DbC as it applies to C++.  Code is provided to add DbC 
style assertions to C++ code.  For the most part the C++ preprocessor 
is not used, with inline methods being used for assertions.  This is 
an interesting approach.  I see only two possible problems.  First, 
I'm not 100% sure the optimizer can reduce such assertions to no-ops 
when assertions are turned off.  At the very least the expression is 
going to be evaluated with this approach.  Second, this prevents us 
from using the __FILE__ and __LINE__ macros effectively.  Inheritance 
is not addressed at all in this article.  The assertions are also not 
configurable.

http://www-
ctp.di.fct.unl.pt/~pg/Tools2000/Another_Mediocre_Assertion_Mechanism_f
or_C++.pdf

This paper defines a complete (well, as near as can be done in C++) 
DbC system in C++.  Pre/post-conditions, class invariants, loop 
invariants and checks included.  Inheritance is addressed, at least 
as much as is possible with out compiler support of DbC, and 
unfortunately it requires some discipline to get right.  This library 
also avoids the preprocessor, with the same drawbacks I listed 
above.  All assertion functionality is found in an Assertions class.  
To declare invariants one must inherit their class from Assertions 
and override a virtual invariant() method.  This is needlessly 
intrusive on class heirarchies.  There's also a problem with 
invariants being checked too often since ensure() checks the 
invariant with each call.  Selectively enabling levels of assertions 
is mentioned, but not addressed.  The ability to check "old" values 
in postconditions is addressed, but only for int types.  The paper 
mentions using a "polymorphic map", but no help is given in 
implementing such a concept.  It would likely be easier to make use 
of the C++ preprocessor to acheive the same effect.  The library also 
includes loop variants and invariants, something I have not included 
in Boost.Assertions.

I'd love to hear other's comments or to hear about other references 
on this topic.

Bill Kempf