Re: [boost] Infinite precision integer draft

From: Topher Cooper (topher_at_[hidden])
Date: 2006-06-02 18:40:00

I don't think that it is that important to have unsigned_integer, but 
this argument against it doesn't stand up:

1) Unsigned integer is not just an arbitrary restriction on range but 
an important concept in its own right.  Its use clarifies intent.  In 
my opinion, for example, it is a common, though minor, programming 
error to use "int" rather than "unsigned int" when you intend to 
express cardinality of something (e.g., the size of an array).  The 
only real justification otherwise is to allow such practical "tricks" 
as testing if a decreasing index is less than 0.

2) The extra data type, assuming that the design error of deriving 
unsigned_integer from integer is avoided, would add complexity for 
boost maintainers but virtually none for users.  It is, after all a 
logical extension of the built in types -- it takes the user all of 5 
seconds to understand it, if that.  Good library design is 
user-centric.  Developer-centric design is the root of a great deal 
of evil.  Lack of development/maintenance resources is, of course, a 
valid argument, but this is a completely different issue than that of 
the evils of unnecessary complexity.

3) Normal use of an unsigned integer type will never "try" to produce 
a negative result -- its not a meaningful concept, so if you play by 
the rules it doesn't happen.  You certainly would never try to negate 
a cardinality (how often do you write code that says "If this string 
contains 27 characters then I want another one containing -27 
characters?).  Subtraction does have to be done with care, but in 
most cases the issue of subtracting a larger from a smaller doesn't 
come up.  Subtraction generally appears, sometimes subtly so, as a 
computation of the size of the complement of a subset within a larger 
set.  If you are dealing with where you would want to use unsigned 
integers and you unwittingly do subtract a larger from a smaller 
value -- if your program logic does not protect you from it -- than 
you better have an exception.

4) If the exceptions are exceptional than in most systems it is very 
much more expensive to do an explicit test than to set up to handle 
an exception.

Topher Cooper

At 04:09 PM 6/2/2006, you wrote:
>Unsigned integers shouldn't exist.  If the programmer wants to check
>whether the number is greater than 0, or greater than 42, he can do it
>himself a lot faster than a try{} catch{} block in terms of both
>programming and runtime.  Creating the extra datatype would add
>completely unnecessary complexity to the situation.     Unnecessary
>complexity is the root of all evil.
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