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Subject: Re: [boost] [Review:Contract] Some questions
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2012-08-27 02:33:16

Le 27/08/12 03:20, Lorenzo Caminiti a écrit :
> On Sun, Aug 26, 2012 at 10:04 AM, Vicente J. Botet Escriba
> <vicente.botet_at_[hidden]> wrote:
>> Le 26/08/12 11:16, Vicente J. Botet Escriba a écrit :
>> Hi,
>>> First of all, thanks Lorenzo for your work on pre-processor programming.
>>> With this library, you have showed to me how far the pre-processing can go
>>> in terms of expressiveness.
>>> I have some questions before doing a complete the review:
>> Hi again,
>> more comments and questions follows
>> = member initializers =
>> Why the following limitation?
>> "Unfortunately, when member initializers are specified, the constructor body
>> must be defined together with its declaration and contract."
> See note 34:
I have read these notes. This seems to me a *hard* limitation and I
would like you explain here deeply and broadly why, maybe someone could
give you some ideas on alternatives.
>> = C++03 limitations =
>> It would be great if you add a section/table with all the limitations, as
>> e.g. these ones
> Will do.
Maybe you could already replay by completing the list below, and for
each one if there is a possibility/plan to remove it.
>> * Function and array types cannot be directly used as function parameter
>> types within the contract macros ...
>> * Each function parameter must always specify both its type and its name
>> (parameter names can instead by omitted in usual C++ declarations).
>> * All tokens must be specified in the fixed order listed in the Grammar
>> section (it is not possible to specify postconditions before preconditions,
>> |volatile| before |const| for member functions, etc).
>> * Unfortunately, this library does not allow to specify contracts for
>> unions.
>> * Unfortunately, when member initializers are specified, the constructor
>> body must be defined together with its declaration and contract
>> and use some kind of as Warning or Important when documenting them.
>> = use of deferred =
>> IMO deferred is related to the time dimension, while I think you are using
>> it on the space dimension. "The function body definition can be separated"
>> is OK, but deferred :(
> I tough deferred is standard terminology in this context (I even
> double-check it somewhere a couple of years back)... maybe I'm
> wrong... I'm happy to use whatever the standard terminology is for a
> function that is defined in a place different from which it is first
> declared.
Maybe a native English could replay to this point.I'm not really sure my
interpretation is correct.
>> = _BODY macros =
>> Why do you need to make a difference between CONTRACT_FREE_BODYand
> See note 32:
This let me think that for uniformity it would be an alternative to have
>> What if the user uses CONTRACT_FREE_BODYwhen it should use
>> CONTRACT_MEMBER_BODY? It will not have the associated class invariants.
> No, but when you partially disable contracts you might get
> compiler-errors like "function ...XbodyXpush_back is not defined...".
This is not enough. The user would need to test her application using
several combinations, which is not admissible.
>> The user will see this error very late when she realize that the function is
>> breaking a class invariant (by other means).
>> I think it will be better if the syntax forces an error in this case. What
>> about
>> template< typename T, T Default >
>> bool CONTRACT_MEMBER_BODY((natural<T, Default>),equal) ( natural const&
>> right )
>> const
>> {
>> return not less(*this, right) && not greater(*this, right);
>> }
>> This will make more homogeneous |CONTRACT_CONSTRUCTOR_BODY|,
>> What do you think?
> It used to be MEMBER_BODY(func_name), then it was
> MEMBER_BODY(class_type, func_name), and now it's back to
> MEMBER_BODY(func_name) ;) See note 47:
I don't see how this note respond to my point. Could you clarify, please?
>> = ( void ) || empty macro parameters =
>> |
>> For projects that don't care about portability, or just use compilers that
>> supports the | empty macro parameters it will be great if they can use ()
>> instead of ( void ) to represent no parameters.
>> Could you provide this?
> On a decent pp (g++), ( ) should work instead of ( void ). The lib
> implementation should supports both (even if this complicates the
> implementation and I didn't fully test () ) -- I'll state this in the
> docs.
Do you plan to support it?
>> = _TPL macros and performance =
>> Could you give some figures of the gain of the change of introducing the
>> _TPL macros?
> No, I don't have the numbers :( Now it'll be too much work to
> implement the without _TPL case to compare... However, the without
> _TPL implementation created an extra 4 template functions for each
> user defined functions.
How many non-template functions are created for the non _TPL implementation?

> In the _TPL case the extra 4 functions are
> template functions only when the user function is also a template.
>> = Static assertions =
>> What is the interest of disabling static assertion when
>> defined?
> Not sure... I wondered this myself. I guess such static assertions for
> pre/post/inv are a new feature so it's just my best guess. Allowing to
> disable a precondition static assertion when you disable precondition
> made some sense to me -- otherwise, what will be the difference
> between a static assertion in preconditions, postconditions, or class
> invariants? or even within the body itself? However, I thought about
> this and I wan't 100% sure either way... I'm happy to discuss this
> requirement more.
Disabling preconditions/postconditions or invariants has a sense as
these are run-time checks, but static assertions as checked at compile-time.
>> = return =
>> ^" *Rationale.* The result type needs to be copyable in order for the
>> function itself to return a value so this library can always evaluate return
>> value declarations."
>> This is only true if rvalue references are not supported. Otherwise, for
>> MovableOnly types the variable used to store the return value could be a
>> rvalue reference and move semantics should be applied.
>> Even if you don't support C++11, the user can use Boost.Move.
> I think so. I don't mention rvalues at all (emulated nor C++11) in the
> docs... I can add a few notes about rvalues when supporting C++11.

As you are copying the return value, the user can not use move
semantics, and the library need to take care of this explicitly.
Do you plan to take care of move semantics before release (if accepted)?


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