Create std::array from variadic template

Question

I'd like to achieve something like that:

#include <string>
#include <array>

enum class MyEnum{
  A,
  B,
  C
};

template<MyEnum... Args>   
class MyClass{
  public:
    MyClass()
    {
    }
  private:
    std::array<MyEnum, sizeof...(Args)> array;   
};

Now I have an array, which can hold all passed to template values. But how can I populate this array with template parameters?

@MiniKarol please look at my updated answer. The accepted answer is not as efficient or pretty as the updated one (thanks to Xeo). — Seth Carnegie
– Seth Carnegie, Commented Apr 28, 2012 at 17:09

Xeo · Accepted Answer · 2012-04-28 17:16:08Z

6

If what you are wanting is to put all the MyEnum values into array, then you can ~~unpack them into an initialiser list and initialise array with it~~ initialise it with direct initialisation:

MyClass() : array {{ Args... }} { }

You need a fairly new compiler to use this syntax, however.

Thanks to Xeo for correcting my answer.

edited Apr 28, 2012 at 17:16

Xeo

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answered Apr 28, 2012 at 16:12

Seth Carnegie

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8 Comments

n. m. could be an AI Over a year ago

This won't work as std::array does not have a constructor that accepts an std::initializer_list.

Seth Carnegie Over a year ago

@n.m. oh, that seems weird. Why does array<int, 4> a { 1, 2, 3, 4 }; work then?

Xeo Over a year ago

@Seth: Direct initialization, std::array is a POD type. You can use that same syntax in the member initializer btw.

Seth Carnegie Over a year ago

@Xeo oh that explains it then, I didn't know array was POD. Thanks. What do you mean "you can use that same syntax in the member initializer"?

Dejwi Over a year ago

Thank it works perfectly but I have to enclose Args... within two pairs of brackets - MyClass(): array{{Args...}}{}

|

n. m. could be an AI · Accepted Answer · 2012-04-28 16:42:25Z

0

MyClass()
{
    std::initializer_list<MyEnum> il( {Args...} );
    std::copy (il.begin(), il.end(), array.begin());
}

answered Apr 28, 2012 at 16:42

n. m. could be an AI

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