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Pietro
Pietro

Reputation: 13162

How to force a template parameter to be an enum or enum class?

I implemented the following class:

template<typename Enum>
class EnumDescription
{
    //TODO Force Enum to be an enum type

public:
    static std::string get( const Enum val );
};

This works as expected, but now I would like to constraint the Enum template parameter to be an enum/enum class only.

Upvotes: 5

Views: 3059

Answers (1)

StoryTeller - Unslander Monica
StoryTeller - Unslander Monica

Reputation: 170065

Depends on your flavor of C++.

C++17

The most easy to write way is a static assertion

template<typename Enum>
class EnumDescription
{
    static_assert(std::is_enum_v<Enum>);

public:
    static std::string get( const Enum val );
};

C++20

You can specify an ad-hoc constraint on the template

template<typename Enum> requires std::is_enum_v<Enum>
class EnumDescription
{

public:
    static std::string get( const Enum val );
};

or, probably for the better, with a reusable concept

template<typename E>
concept EnumType = std::is_enum_v<E>;

template<EnumType Enum>
class EnumDescription
{

public:
    static std::string get( const Enum val );
};

Upvotes: 10

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