NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part2/10468

Text File | 1996-08-05 | 2.6 KB | 72 lines

Newsgroups: comp.lang.c++
Path: night.primate.wisc.edu!relay!news
From: Tom McLintock <tmclint>
Subject: An (Ada-style) enum template class??
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Organization: Naval Surface Warfare Center - Dahlgren Div.
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Date: Fri, 8 Mar 1996 03:28:01 GMT
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Has anyone made a general-purpose, powerful enum "container" class?  This would
create a class containing full functionality for an enum you give it, or a list
of enum values you give it.  With a variable of such a "type", you could

- read an enum value from a text file into the variable and write its value to
  the screen (not just its numeric int-value, but a string representation of
the
  value's name)

- increment and decrement the variable with ++ and --, and throw an exception
  when you go off one end of the enumerated values

- get the number of enum values so you can, say, define an array indexed by
  the enum class

- add values to the enum class when deriving a new class from the base enum
  class

- of course use the variable as an lvalue or an rvalue that works just like a
  normal enum variable

- all this without having to specify the values of the enum to the class as
  both an actual enum type and an array of string representations of the enum
  values.

I've come up with solutions to some of these problems using, among other
tricks,
BIG #define macros and bizarre non-C/C++-looking syntax, but there MUST be a
better way!  All of the above features are useful and are in Ada (a language
I'm
not generally fond of otherwise).  Bjarne Stroustrup seems to think that an
enum
shouldn't have to do all this, from what I've read, but my experiences with Ada
suggest otherwise.

BTW, I've found that the humble #define still has a lot of usefulness in C++,
in
spite of what many writers claim.  For example, I wrote a trace macro that
lets you write, for example,
TRACE(i _ x _ str); // i, x, and str are int, float and char* variables
and when the program runs, the output from the TRACE call is something like
###filename.C (line 234)###
    i: 42
    x: 3.14159
    str: "Hello world"
Let's see anyone do that in C or without using the preprocessor!

--
  - Tom McLintock
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