Re: Unsignedness of std::size_t
Kaba wrote:
It communicates a precondition >= 0. Why should this precondition be
communicated in compile-time, when all the other preconditions are
communicated run-time? Why should this precondition be given more weight
than the others?
What others are you referring to? There are many requirements that are
checked at compile time. Most people think that's a good thing.
By a precondition here, I mean checking the validity of a passed-in
variable. That is purely a run-time issue. Other requirements can be
anything: "n should be even", "n should be prime", "text must contain
the string 'rabbit'", etc.
Robust code calls functions with valid arguments unless the function is
specified to check for invalid values. If code calls a function with
invalid values (i.e. negative integer values when the function calls for
a non-negative value), the code is wrong.
If a code calls functions with valid arguments, it is already correct
(w.r.t this issue). When developing, this is more than often not the
case. Silently entering a bad state by not checking preconditions is
among the worst things you can do.
If a function f is specified as taking any value from 0 to UINT_MAX,
inclusive, you write it with an argument of type unsigned. There's no
precondition to check: the argument will always be valid. If someone
calls it with an argument of -1 because they subtracted a couple of
numbers and didn't bother to check that the result made sense, there's
no precondition that f can check to find that. Now, sure, you could
rewrite the interface with some larger integral type, in order to
artificially produce something that you could check, but at some point
you have to leave it to programers to do things right. Libraries should
be written to express what they do, not what errors careless programmers
might make.
--
-- Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com)
Author of "The Standard C++ Library Extensions: a Tutorial and
Reference." (www.petebecker.com/tr1book)
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