Re: [boost] [contract] Without the macros

On Wed, Jun 15, 2016 at 2:21 PM, Klaim - Joël Lamotte wrote:

On 15 June 2016 at 23:15, Lorenzo Caminiti wrote:

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On Wed, Jun 15, 2016 at 8:47 AM, Matt Calabrese wrote:

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On Jun 15, 2016 08:31, "Lorenzo Caminiti" wrote: Have you followed any of the recent papers regarding language-level contracts for C++?

No... but I should definitely take a look! Do you have a link to the proposal to get me started?

Here is the last version of the proposal: http://open-std.org/JTC1/SC22/WG21/docs/papers/2016/p0380r0.pdf

I always thought it'd be great to have contracts added to the core language... if not for anything else, for a more concise syntax and compiler optimizations. Unfortunately I found this P0380 proposal largely inadequate. In my opinion/experience, the following are major issues with P0380: 1. Complete lack of class invariants. In my experience, class invariants are essentially as important as preconditions when programming contracts for objects. 2. No old values for postconditions. In my experience, most postcondition assertions cannot be programmed without old values. 3. If I understand it correctly, the rule that "the contracts of every declaration of a function must be (ODR) identical" (P0380 section 4) essentially prevent subcontracting. Class invariants, postcondition old values, and subcontracting are key aspects of contract programming. A framework that does not support those is not really a contract programming framework, it's essentially just a bit more than `assert()`. Maybe that was the intent of P0380 to be just a bit more than `assert()`... but is that useful or it's best to just use `assert()` at that point (maybe within #ifdef to emulate the default/axiom/audit levels)? N1962 (http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1962.html) was a solid proposal for adding Contract Programming to C++. Why not accepting that proposal (maybe with the attributes syntax introduced by P0380)? I might write to P0380 authors with some of these notes. Thanks, --Lorenzo P.S. Of course, these P0380 gaps will make Boost.Contract useful even on C++1z (say if you want to do basic stuff like using old values in postconditions, programming a class invariants, or even more complex stuff like using subcontracting).