Template parameter: class enum, class or enum
Consider the following class:
template <class Endianness>
class bitcode
{};
C Endianness
, which may be? default_endianness
, little_endian
Or big_endian
.
The question is this: according to C ++ 14 and the following C ++ 17, what will / will be the best and most common? (by general I mean those used (or will be used) by the standard library or boost
. (+ and why?)
// The enum option
enum enum_endianness {default_endianness, little_endian, big_endian};
// The enum class option
enum class enum_class_endianness {default_endianness, little_endian, big_endian};
// The class option
class class_default_endianness{};
class class_little_endian{};
class class_big_endian{};
(Note: of course the declaration bitcode
will depend on the preferred option.)
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The choice is somewhat subject, but if you want to use it as a template parameter (for your class template, for example bitcode
) I would stick with the class / struct tags. This tends to make templating easier to program than mixing things templated by type with templated by specific constant values.
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enum class
is the most appropriate. It is a type-safe, restricted enumeration. You can compare values using an operator ==
, and you can apply specialization and subtraction using template parameters.
enum
is an unlisted enumeration. They are mostly seen as a backward compatibility feature with C ++ 98 and C. Values will be implicitly converted to int
, but those integer values will be meaningless.
class
gives you the submit tags. While this will work, you will have no ==
and operators !=
, which can lead to overuse of templates and overloads.
Another pattern to consider is the type pattern: a class that contains static data members and functions, so you don't need to add additional template parameters.
enum class endianness {little_endian, big_endian};
class little_endian_traits {
static const enum endianness endianness = endianness::little_endian;
};
class big_endian_traits {
static const enum endianness endianness = endianness::big_endian;
};
typedef little_endian_traits default_endian_traits; // depending on platform
template< class traits >
class bitcode;
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