Re: [boost] New Boost.XInt Library, request preliminary review

Subject: Re: [boost] New Boost.XInt Library, request preliminary review
From: Chad Nelson (chad.thecomfychair_at_[hidden])
Date: 2010-03-28 23:56:43

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On 03/28/2010 10:13 PM, Scott McMurray wrote:

>> Blockable exceptions are an XInt library thing, which I added
>> because people are asking for them. See the XInt documentation, the
>> page labeled "Exceptions and Exception Blocking"
>> (ref_exceptions.html).
> 
> Then the obvious question is, "Why isn't overflow blockable"?

And it's an excellent question. The only justification for making it
non-blockable is that, if it were blockable, then nearly every function
in the library could potentially return a Not-a-Number value, and you'd
have to check for it constantly when blocking exceptions. That would
defeat the intended purpose of the exception-blocking mechanism (see
below). As it's not, you only have to check for the Not-a-Number value
on the few functions that can throw a blockable exception.

> If the point is to be useful when exceptions are off, they should
> all be able to generate special values instead of throwing. 

There's no other logical response if there's no cryptographically-secure
random number generator, and the user asks the library to instantiate
one. (That's not in the version that was uploaded to the Boost Vault
yet.) And it's debatable whether there's any other consistent and
mathematically logical way to handle passing Not-a-Number values to
functions that return anything but xint::integers.

The mechanism isn't there so that the exception-hating crowd can get
away with avoiding exception-handling. It's there to give the developer
using the library the flexibility to treat its functions as returning
error codes, rather than throwing exceptions, when it would make for
more readable code.
- -- 
Chad Nelson
Oak Circle Software, Inc.
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