Fwd: Re: Is const int a signed integer type?

From: Beman Dawes (beman_at_[hidden])
Date: 2000-10-19 15:55:54

Here is a response to Jesse Jones' query from Mike Miller (the C++ 
committee's core language working group chair).

I'll respond to him suggesting that there is in fact a defect; the readers 
were "knowledgeable" and yet they reached the opposite conclusion.

Regardless of that, no one else has challenged Mike's answers to the 
questions, so I expect his interpretation is what most of the core working 
group believes.

--Beman

 >> Boost has a number of template meta-functions used for
 >> identifying types.
 >>
 >> See http://www.boost.org/libs/utility/type_traits.htm
 >>
 >> They include functions like is_standard_signed_integral and
 >> is_pointer. However there's some question about how these should work
 >> for const types. Section 3.9.1 of the standard says that "there are 
four
 >> signed integer types: signed char, short int, int, and long int". 
Section
 >> 3.9.3 says that these types are cv-unqualified and the cv-qualified
 >> versions are distinct types. This seems to mean that const int is not a
 >> signed integer type. Is this interpretation correct and is it what the
 >> committee intended to say?
 >>
 >> The pointer case is similar: the first sentence in section 3.9.3 can be
 >> read to mean that const pointer types are not pointer types. Is this  A 

 >> interpretation correct?
 >
 >This could be said somewhat more clearly in the Standard, but obviously
 >these interpretations are not what is intended.  The categorization of
 >the various types in 3.9.1 is based on the values each can represent,
 >which in turn is related to its value representation (3.9p4).  3.9.3p1
 >says that "The cv-qualified or cv-unqualified versions of a type... shall
 >have the same representation and alignment requirements."
 >("Representation" includes both object representation and value
 >representation.)  This means that the cv-qualified version of a type can
 >contain exactly the same set of values as its cv-unqualified version.
 >The "int" type is called a signed integral type because its possible
 >values are a subset of the signed integers; because "const int" can
 >represent exactly the same set of values, it also is a signed integral
 >type.
 >
 >Another way of looking at this is that 3.9.3p1 says that the cv-qualified
 >types are "distinct" types, not "unrelated" types, and uses the word
 >"version" to describe them.  A const char "is-a" char with some
 >restrictions on the context in which it can be used, none of which relate
 >to its inherent characteristics.    3.9.1p1 should be read as saying that
 >there are four fundamental signed integer types, each with three
 >(additional) cv-qualified versions.
 >
 >I wouldn't object to seeing better phraseology in the next version of
 >the Standard here, but I think a "close and careful reading" of the
 >existing text is sufficient for a knowledgeable reader to arrive at the
 >correct conclusion, i.e., there is no defect.
 >
 >-- Mike Miller