Re: [boost] Checked Integral Class

From: michael toksvig (michaeltoksvig_at_[hidden])
Date: 2005-09-16 17:22:33

> "Rob Stewart" <stewart_at_[hidden]> wrote in message 
> news:200509162032.j8GKWh51025673_at_shannonhoon.balstatdev.susq.com...
> Consider that the class is used to model, say, permitted voltages
> in an electonic circuit.  Say that an input on the circuit is
> constrained by only being able to support voltages of 2-5V.  (If
> you connect two batteries in series, the voltages add.)  If each
> battery's voltage is expressed with a checked integer of the 2-5V
> range, and their voltages are summed, your result would be a
> checked integer with a 4-10V range.  That exceeds the permitted
> input voltage range and two batteries of 4V each would blow the
> input.  How would you handle that in your model?

given a constrained value type, CV<min, max, policy> and the following:
    CV<2, 5, some_policy> batteryA, batteryB;

you could decide either to do:
    CV<2, 5, compiletime_policy> input = batteryA+batteryB; // compiler will 
kindly alert you to the fact that there is a potential problem here

or, if you are confident the potential problem doesn't occur:
    CV<2, 5, assert_policy> input = batteryA+batteryB; // at runtime, if 
something bad happens, it will assert

>
> In my approach, the result would be a value with a 4-5V range.
> That fits within the 2-5V range and so a successful sum of
> battery voltages doesn't exceed the range of the input.
>
> Unless I've missed something, your approach requires a runtime
> check to see whether the actual result of the addition exceeds
> the input voltage range during some later computation or
> comparison.  My approach catches the range error during the
> addition.
>
> -- 
> Rob Stewart                           stewart_at_[hidden]
> Software Engineer                     http://www.sig.com
> Susquehanna International Group, LLP  using std::disclaimer;
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