Customizing the equality function

ArrayList supports the contains (G item) its equality function can be customized by providing an implementation of EqualDataFunc.

bool same_book (Book a, Book b) {
    return a.isbn == b.isbn;
}

var books = new Gee.ArrayList<Book> ((EqualDataFunc) same_book);

Other delegates such as CompareDataFunc and HashDataFunc apply to other Collections.