How to create an array constructor for my class?

Question

I would like to create a constructor, which is similar to the int array constructor: int foo[3] = { 4, 5, 6 };

But I would like to use it like this:

MyClass<3> foo = { 4, 5, 6 };

There is a private n size array in my class:

template<const int n=2>
class MyClass {

    public:

        // code...

    private:

        int numbers[n];

        // code...

};

The type int[3] is not a class type, so it doesn't have a constructor. It can be initialized, but not via a constructor call. — Kerrek SB
– Kerrek SB, Commented Jan 15, 2016 at 12:36

Community · Accepted Answer · 2017-05-23 12:17:00Z

18

You need a constructor that accepts a std::initializer_list argument:

MyClass(std::initializer_list<int> l)
{
    ...if l.size() != n throw / exit / assert etc....
    std::copy(l.begin(), l.end(), &numbers[0]);
}

TemplateRex commented...

You might want to warn that such constructors are very greedy and can easily lead to unwanted behavior. E.g. MyClass should not have constructors taking a pair of ints.

...and was nervous a hyperactive moderator might delete it, so here it is in relative safety. :-)

edited May 23, 2017 at 12:17

CommunityBot

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answered Jan 15, 2016 at 12:16

Tony Delroy

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2 Comments

TemplateRex Over a year ago

You might want to warn that such constructors are very greedy and can easily lead to unwanted behavior. E.g. MyClass should not have constructors taking a pair of ints e.g.

TemplateRex Over a year ago

see here for greedy moderation.

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