Is it possible to create constructor-extension-method ? how?

Is it possible to add a constructor extension method?

Sample Use Case

I want to add a List< T > constructor to receive specific amount of bytes out of a given partially filled buffer (without the overhead of copying only the relevant bytes and so on):

...
public static List<T>(this List<T> l, T[] a, int n)
{
    for (int i = 0; i < n; i++)
       l.Add(a[i]);
}
...

so the usage would be:

List<byte> some_list = new List<byte>(my_byte_array,number_of_bytes);

I've already added an AddRange extension method:

public static void AddRange<T>(this List<T> l, T[] a, int n)
{
   for (int i = 0; i < n; i++)
       l.Add(a[i]);
}

I want to do it as a constructor too. Is it possible? If yes - how?

Solution 1:

No, but if you changed your AddRange signature to return the list instance, then you could at least do

var list = new List<int>().AddRange(array, n);

which imho is probably clearer than overloading the constructor anyway.

Solution 2:

SWeko's answer is basically correct, though of course the article he links to is about extension properties rather than extension constructors.

We also did a rough design for extension constructors at the same time as we did extension properties; they would be a nice syntactic sugar for the factory pattern. However, they never got past the design stage; the feature, though nice, is not really necessary and does not enable any awesome new scenarios.

If you have a really awesome problem that extension constructors would solve, I'd be happy to hear more details. The more real-world feedback we get, the better we are able to evaluate the relative merits of the hundreds of different feature suggestions we get every year.