Abbreviated Syntax to define a std::vector of class enum values in C++

Question

Due to my inability to find an answer or the right words to search for I ask here:

I have a (lengthy) class enum defined by

enum class SomeLongName { Foo = 1, Bar = 7, FooBar = 42 };

The only way I know to define a vector of those is:

#include <vector>

enum class SomeLongName { Foo = 1, Bar = 7, FooBar = 42 };

int main() {
  std::vector<SomeLongName> v1 = {
    SomeLongName::Foo,
    SomeLongName::FooBar
  };
  return 0;
}

Is there a way (alternative abbreviated syntax) to use a class enum and don't need to rewrite SomeLongName:: for each value independently? e.g. something like (not working)

#include <vector>

enum class SomeLongName { Foo = 1, Bar = 7, FooBar = 42 };

int main() {
  std::vector<SomeLongName> v1 = (SomeLongName::) { Foo , Bar };
  return 0;
}

In case this matters: I am using MSVC 2019, amd64 (64bit), C++17 on windows 10 64bit

Note: using a typedef like suggested in this stackoverflow discussion thread is not actually what I want or am asking for

Pre-C++20 using enum SomeLongName;, you can also use a function local using E = SomeLongName; to shorten the name. — Eljay
– Eljay, Commented May 12, 2021 at 14:29

Argishti Ayvazyan · Accepted Answer · 2021-05-12 09:31:08Z

5

C++20 added using enum X syntax, which does what it looks like.

#include <vector>

enum class SomeLongName { Foo = 1, Bar = 7, FooBar = 42 };

int main()
{
    using enum SomeLongName;
    std::vector<SomeLongName> v1 = { Foo, Bar };
    return 0;
}

In previous versions, you can use an enum instead of an enum class.

answered May 12, 2021 at 9:31

Argishti Ayvazyan

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2 Comments

mjhalwa Over a year ago

Ah thanks that looks promising. I found it both in the msvc and general c++ supported features per compiler overview being supported by msvc 2019 16.4. But eventhough I have version 16.7 installed I get compiler error (An identifier was expected translated from German) for using enum SomeLongName;, when building via cmake using set(CMAKE_CXX_STANDARD 20) and set(CMAKE_CXX_STANDARD_REQUIRED ON)

Argishti Ayvazyan Over a year ago

You are welcome. I have tried on Visual Studio 16.9.4. Building via CMake using set(CMAKE_CXX_STANDARD 20) passed successfully. I suppose you need to update your VS.

463035818_is_not_an_ai · Accepted Answer · 2021-05-12 09:39:12Z

2

Pre C++20: Unfortunately no. Its a "feature" of scoped enums that you have to prepend the name of the enum type. However, before scoped enums were a thing, it was common to wrap enums in a class to avoid polluting the namespace. You can still do that:

#include <vector>

struct SomeLongName {
    enum values { Foo = 1,Bar = 7, FooBar = 42};

    static std::vector<values> make_vect() {
        return {Foo,FooBar};
    }
};

int main() {
    auto v = SomeLongName::make_vect();
}

It's not "nice" but it works.

Past C++20: I refer you to this answer.

edited May 12, 2021 at 9:39

answered May 12, 2021 at 9:26

463035818_is_not_an_ai

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3 Comments

mjhalwa Over a year ago

This is indeed not very "nice" and actually also more overhead, and worse to read (i think). But still thanks for sharing.

463035818_is_not_an_ai Over a year ago

@Martin the "overhead" is only poor style. If thats the only way and you absolutely want it, I wouldnt consider it too bad to sacrifice a bit of style

mjhalwa Over a year ago

true, but I don't need it that urgent :)

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