Welcome to the Better Enums tutorials! The code in this tutorial forms a valid program, which you can download and play with. The program runs as part of the automated test suite.
Scope and safety
This tutorial shows some of the safety features of Better Enums: scope, how to control conversions, and the lack of a default constructor.
On balance, Better Enums are in one way less type-safe than enum class, and in another way more type-safe. The first difference in safety is the presence of implicit conversion to integral types. The second difference is the lack of a default constructor. Both of these can be toggled, so you can make Better Enums strictly safer than enum class, or just as safe.
Contents
Scope
You have probably noticed by now that Better Enums are scoped: when you declare
#include <cassert> #include <enum.h> BETTER_ENUM(Channel, int, Red = 1, Green, Blue)
you don't get names such as Red in the global namespace. Instead, you get
Channel, and Red is accessible as Channel::Red. This is no big deal in
C++11, which has enum class. In C++98, however, this typically requires
effort. Better Enums brings scope uniformly to both variants. So, despite the
above declaration, you can safely declare
BETTER_ENUM(Node, char, Red, Black)
and everything will work as expected.
int main()
{
assert((+Channel::Red)._to_integral() != (+Node::Red)._to_integral());Implicit conversion
A major complaint in C++98 is that enums are implicitly convertible to
integers. Unfortunately, that is also true of Better Enums, and I haven't found
a way to forbid the conversions and still have switch case checking.
Better Enums can be made as safe as enum class in C++11, however. If your
compiler supports enum class and you define
BETTER_ENUMS_STRICT_CONVERSION before including enum.h, the following code
will not compile:
Channel channel = Channel::Red;
int n = channel;The reason this is not enabled by default is explained in the reference page on strict conversions.
You can conveniently define the macro on your compiler's command line, or by
creating a little header file that defines it, and then includes
enum.h. You can then include this new header file in your project
everywhere where you would have included enum.h.
Default constructor
Better Enums generate without a default constructor. The purpose is to support the convention where if a Better Enum exists, then it has a valid value. So, if you uncomment this code, the program won't compile:
Channel channel;
If this is too strict for your project, you can relax it as described here.
return 0; }