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Date: Mon, 06 Jan 2003 22:14:35 -0500
From: Hyman Rosen <hyrosen@mail.com>
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Subject: Re: Anybody in US using ADA ? One silly idea..
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Date: 2003-01-06T22:14:35-05:00
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Wes Groleau wrote:
> Does C++ have subtypes and derived types?

No. The only thing of this type available is
class inheritance.

 > But I wish I could
> define things like 'First and 'Last when I create a
> private type for which they are meaningful.

In C++, you can set up arbitrary "attributes" of this
sort by using a technique called traits. You define a
class template, and then specialize it for your type.
Whether to have a common fallback value or not is up
to you. Eg.,

template<typename T> struct DoesIt;
struct Dog;
struct Cat;
struct AEIOU;
template<> struct DoesIt<Dog> { enum { Howl = 1, Yowl = 0, Vowel = 0 }; };
template<> struct DoesIt<Cat> { enum { Howl = 0, Yowl = 1, Vowel = 0 }; };
template<> struct DoesIt<AEIOU> { enum { Howl = 0, Yowl = 0, Vowel = 1 }; };