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Subject: Re: [boost] [Review:Contract] Some questions
From: Lorenzo Caminiti (lorcaminiti_at_[hidden])
Date: 2012-08-26 12:24:49
Hi,
On Sun, Aug 26, 2012 at 2:16 AM, Vicente J. Botet Escriba
<vicente.botet_at_[hidden]> wrote:
> 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.
Welcome :)
> I have some questions before doing a complete the review:
>
> = C++11 compatibility =
>
> * Does the library use c++11 features when available? I was thinking e.g. on
> the emulated virtual specifiers. BTW, I think the "new" virtual specifier
> was removed from the standard, but maybe I'm wrong.
> * I think the library don't allow to declare C++11 specific
> classes/function. E.g
> * variadic templates
> * noexcept functions
> * constexpr functions
> * class/function attributes
The library is written for C++03 for now, while it emulates some C++11
features for C++03, the library doesn't support all C++11 features and
doesn't take advantage (go native) of them when available instead of
the emulated features. I am planning to extend the library to support
C++11 (the declaration syntax should be extendible without any
problem). I've added a ticket
https://sourceforge.net/apps/trac/contractpp/ticket/61
> BTW, I have not see any example using exception specifications using
> 'throws'. Does the library support them?
Yes, for example:
http://contractpp.svn.sourceforge.net/viewvc/contractpp/releases/contractpp_0_4_1/doc/html/contract__/advanced_topics.html#contract__.advanced_topics.exception_specifications_and_function_try_blocks
http://contractpp.svn.sourceforge.net/viewvc/contractpp/releases/contractpp_0_4_1/doc/html/contract__/examples.html#contract__.examples.__cline90___stack__function_try_blocks_and_exception_specifications
http://contractpp.svn.sourceforge.net/viewvc/contractpp/releases/contractpp_0_4_1/doc/html/contract__/grammar.html#contract__.grammar.exception_specifications
> Could you confirm? and if not, could you tell us if you have a plan to
> support them?
>
> = Postconditions result =
>
> "Postconditions can access the function return value by declaring a variable
> of type |auto| and assigning it to the |return| keyword (the variable name
> is arbitrary but |result| is often used)."
>
> What prevent the library to the use of return instead of an auto variable
>
> postcondition( // Postconditions.
> auto old_value = CONTRACT_OLDOF value, // Old value(s).
> value == old_value + 1, // Assertion(s)...
> return == old_value
> )
This won't work if return is not the 1st token:
old_value == return
3 + return
myfync(return)
etc
because there's no way the preprocessor can skip the leading tokens
given that they are unknown :( and they could contain symbols. I will
clarify this point in the rationale.
> instead of
>
> postcondition( // Postconditions.
> auto result = return, // Result value.
> auto old_value = CONTRACT_OLDOF value, // Old value(s).
> value == old_value + 1, // Assertion(s)...
> result == old_value
> )
>
> =Constant assertions =
>
> I would expect that the old are always const so the following
>
> postcondition(
> auto old_even = CONTRACT_OLDOF even,
> auto old_odd = CONTRACT_OLDOF odd,
> // `[old_]even` and `[old_]odd` all `const&` within
> assertions.
> const( even, old_even ) even == old_even + 2,
> const( odd, old_odd ) odd == old_odd + 2
> )
old_... are const but you need to specify them in const( ... ) so they
can be accessed by the constant-assertion boolean condition:
const( var1, var2, ... ) boolean-condition-using-var1-var2-...
only global/static variables and var1, var2, etc can be used by
boolean-condition-using-var1-var2-... The docs are not clear abut this
point, I'll clarify it.
> should be rewritten without loss of semantics as
>
> postcondition(
> auto old_even = CONTRACT_OLDOF even,
> auto old_odd = CONTRACT_OLDOF odd,
> // `[old_]even` and `[old_]odd` all `const&` within
> assertions.
> const( even ) even == old_even + 2,
> const( odd ) odd == old_odd + 2
> )
>
>
>
> = Oldof =
>
> As the old of value must be declared using a variable, using a specif oldof
> keyword that will replace
>
> auto old_size = CONTRACT_OLDOF size(),
> by
>
> oldofold_size = size(),
This wont' work because the pp can't separate the trailing size()
expression for the rest because it can't deal with unknown tokens and
symbols like "size()" or "old_size". The expression:
auto old_size = CONTRACT_OLDOF size()
is parsed into type "auto", assignment "old_size =" (note that the pp
can't separate the = because it's a symbol and that required lots of
tricks to be handled correctly...), and the expression "size()". I
need all these separate traits to handle old-values while:
oldofold_size = size()
and even:
oldof old_size = size()
can't separate "old_size = size()" into "old_size" and "size()". The
macro CONTRACT_OLDOF expands into )( so at some point in the
CONTRACT_FUNCTION expansion this:
CONTRACT_FUNCTION( ... auto old_size = CONTRACT_OLDOF size() ... )
expands to (auto is know or wrapped within parenthesis the user):
(auto) (old_size =) (size())
which is ultimately a sequence and it can be handled by the pp.
> could simplify the syntax. What do you think?
>
> Some minor points:
>
> * Why do you use( void ) instead of () in the functions without
> parameters? e.g.
>
> public: bool empty ( void ) const { return vector_.empty(); }
Because MSVC pp gets confused with () even on C++11. On G++ you can
use () but the code might not always compile with MSVC :(
> Some suggestions:
>
> * Use 2 spaces indentation instead of 4 could reduce the width of the page,
> in particular when you use several columns.
> * The use of'int const' as return type is verbose and could be replaced by
> just int.
Thanks,
--Lorenzo
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