Re: [Boost-users] [review][constrained_value] Review of Constrained Value Library begins today

Subject: Re: [Boost-users] [review][constrained_value] Review of Constrained Value Library begins today
From: John Maddock (john_at_[hidden])
Date: 2008-12-03 12:02:39

Mathias Gaunard wrote:
>> I think this is wrong.
>> Providing an invalid value should be a non-recoverable programming
>> error. Non-recoverable means it should abort the program, and
>> programming error means it should only be enabled in debug mode.
>> i.e. an assert is the best choice to assert the preconditions are
>> met.

I couldn't disagree more: that would negate the whole point of the library.

I'm not saying that the design choices you want may not be valid in some 
situations, just that you're asking for a different library.

Indeed if it's absolutely essential to the proper functioning of the 
software that a value fall within certain constraints, turning off 
assertions in release mode, or indeed aborting, may not be viable options 
(think embedded program control software).  Would you really want your 
software to crash if it detected a negative velocity for your car?  (or your 
car to crash if the software fell over?).

This library lets you choose what actions happen on constraint-failure, 
including assert or no-op actions if that's what you really want.  But I 
suspect most users of the library will be looking for something that will 
allow them to write fault-tolerant code.

>> Apart from that, wouldn't it be more interestin, when multiplying a
>> bounded_int<int, 0, 23> by 2, to yield a bounded_int<int, 0, 46>
>> instead of attempting to keep the object with the same constraint?

Interesting, as in "may you live in interesting times"?  ;-)

John.