Re: [boost] safe integer library -- the scope

14 Dec 2015


      On December 14, 2015 3:23:28 PM EST, Robert Ramey  wrote:
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On 12/14/15 11:15 AM, Rob Stewart wrote:
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On December 14, 2015 11:39:50 AM EST, Robert Ramey 
wrote:
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> runtime checking is required.  Here we've achieved the holy
grail:
>
> a) guaranteed correct arithmetic result
> b) no runtime overhead.
> c) no exception code emitted.
> d) no special code - we just write algebraic expressions
>
> This is the true motivation for safe_..._range
Why isn't that the behavior of your safe type in the first place?
it is
I'm confused. If that's the behavior of safe, why do you need
safe_..._range?
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That is,
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what benefit does your safe type offer that it shouldn't just be
supplanted
by the range type?
safe<T> can be used as a drop in replacement for T . safe...range
cannot.
Why not?
It's really syntactical sugar
everywhere I int I can now use safe<int>.  Without this, I'd have to
write
safe_integer_range<
     std::numeric_limits<int>::min(),
     std::numeric_limits<int>::max()
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which would become tedious.
I showed a safe class template, below, that defaulted the min and max to those values, and you said that was "exactly what safe<T> is". If yours has those defaults, then there is no such tedium.
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However, since min() and max() are now constexpr, that all can be
collapsed into a single template with three parameterizing types:
the
underlying type, the minimum, and the maximum:
template
<
     class T
   , T Min = std::numeric_limits<T>::min()
   , T Max = std::numeric_limits<T>::max()
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class safe;
That's exactly what safe<T> is.
Why doesn't that suffice for all use cases?
Hmm - can I rephrase this question as
what is safe_range good for?
answer - lot's of things
b) The main driver is a case like the following:
int a, x
int y = a * x; // possible error
safe<int> a, x;
safe<int> y = a * x; // possible error - but checked at runtime
safe_integer_range<-10, 10> a, x;
safe<int> y = a * x; // no runtime checking necessary
though of course something like the following would be useful
using minutes_t = safe_unsigned_range<0, 59>
There are other examples in the documentation.
I'd expect that from the one safe class template. I'm missing something.

___
Rob

(Sent from my portable computation engine)