Specifying constructor constraint for Generic Parameter [duplicate]

Answer 1

You can't constrain generic type constructors in this way (only to require a parameterless constructor), but you could take a delegate to do the construction:

public static IList<T> ConvertTo<A, T>(this IEnumerable<A> list, Func<A, T> constructionFunc)
{
    return list.Select(constructionFunc).ToList();
}

And use it like this:

var IList<T> converted = someSequence.ConvertTo(a => new T(a));

Answer 2

Unfortunately, this isn't allowed in C#. You can have a new() constraint that forces the type to have a default constructor, but that is the only constructor related constraint supported by .NET.

Your best option is probably to define an interface you can use, and constrain to the interface. Instead of trying to set the object at construction, you can have an "Initialize" style method that takes the "A" object, and call that.