Re: [boost] [contract] diff n1962

Subject: Re: [boost] [contract] diff n1962
From: Lorenzo Caminiti (lorcaminiti_at_[hidden])
Date: 2010-04-11 10:16:17

Hello all,

On Thu, Apr 8, 2010 at 7:26 PM, Lorenzo Caminiti <lorcaminiti_at_[hidden]> wrote:
> Below is a summary of the differences between Boost.Contract and the
> Contract Programming  C++ standard proposal n1962. I know some of the
> authors of n1962, and also of its previous revisions, are on this
> mailing list -- I hope that they can provide comments at least.

Thank you very much for all your replies. I will address your comments
and modify Boost.Contract as needed. Before that however, I have one
additional question on constructors -- for everyone and again
especially for the n1962 authors.

CONSTRUCTORS
Does n1962 require constructor preconditions to be checked before or
after the execution of the member initialization list?

>From n1962 section 4.2.2: <<Constructors behave much like member
functions. This means that a constructor can have a precondition and a
postcondition. The precondition may not reference member variables.>>.

Boost.Contract checks preconditions after the member initialization:
member-init > static-inv > pre > body > static-inv > inv > post.
However, when asked why I could not really come up with an explanation
but that it would be difficult to implement Boost.Contract
differently...

Eiffel checks "default" > pre > body > inv > post. Where "default"
essentially means that member variables are in a default state. I
think, this is similar to executing the member initialization before
checking preconditions but not quite the same because default member
values for Eiffel are essentially just Void. C++ instead can assign
more complex values in the member initialization list. Because these
values can be functions of the constructor input parameters, you can
make the argument that C++ preconditions should be checked before the
member initialization list so to validate the constructor parameters
before they are used to initialize the members.

Thank you.
Lorenzo