Re: [Boost-users] [boost] [review][constrained_value] ReviewofConstrainedValueLibrary begins today

Subject: Re: [Boost-users] [boost] [review][constrained_value] ReviewofConstrainedValueLibrary begins today
From: Robert Kawulak (robert.kawulak_at_[hidden])
Date: 2008-12-10 16:48:04

> From: Gordon Woodhull
> On Dec 9, 2008, at 9:21 AM, Jesse Perla wrote:

> > I absolutely agree that if this library was purely for bounds  
> > testing, managing invariants, etc, that predicates are 
> sufficient.   
> > But for high performance numerics, that is not what would happen.   
> > First of all, you would turn off automatic testing at runtime.
> 
> I think this is another good reason to allow disabling of these  
> asserts specifically (as opposed to disabling all boost asserts).

I think Jesse meant turning off constraint checking in general, not only the
invariant asserts.

> > But one of the key value of this library, in both 
> release/debug, for  
> > those examples is to get information about the bounds and 
> intervals  
> > from the type itself for generic algorithms.  A predicate as a  
> > function can test assignment, but it can't give back 
> structured data  
> > for these algorithms.  If you can show me how the testing 
> predicate  
> > can be easily queried within this framework for the type metadata  
> > itself(e.g. a list of intervals), then I will shut up.

Well, just the way you query within_bounds predicate to get the values of bounds
etc. The point is to provide a wrapper for a predicate which allows you to
access all its data, but "overwrites" the invocation operator to always return
true. Maybe it could look like this (not tested, not contemplated much):

template<typename P>
struct true_predicate_wrapper : public P
{
        true_predicate_wrapper() : P() {}
        true_predicate_wrapper(const P & p) : P(p) {}

        template<typename V>
        bool operator () (V) const { return true; }
}

You can use P predicate (containing all the data like intervals list) in debug
mode and true_predicate_wrapper<P> in release mode to retain all the
information, but get rid of constraint checks.

Best regards,
Robert