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