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From: Hyman Rosen <hyman.rosen@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: What's wrong with C++?
Date: Wed, 16 Feb 2011 12:07:02 -0800 (PST)
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Date: 2011-02-16T12:07:02-08:00
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On 2/16/2011 2:36 PM, KK6GM wrote:
> Will a C++ compiler will reject this?
>
>    enum {Red, Green, Blue};
>    int x = Red + Green;
>
> You might argue that this is a different issue, but I'm still curious.

No, it will not, and it is a different issue. The particular
issue here is that enumeration literals in C and C++ have
automatic conversion to integer (but not the other way in C++).

Also, enumerations in C were intended to represent bit masks
as well as sets of values, so in both C and C++ a variable
of enumeration type may correctly hold values that represent
the bitwise-or of any number (including 0) of the literals.
This is legal C++:

    struct DamageType {
        enum E { Fire = 1, Acid = 2, Lightning = 4, Poison = 8 };
    };

    DamageType::E what_my_dragon_can_do =
        DamageType::E( DamageType::Acid | DamageType::Poison );

    DamageType::E what_your_wimp_can_do = DamageType::E( 0 );

A plausible case can be made that the original incorporation of
enum into C should have distinguished between masks and sets, but
that opportunity is long gone.