When no initializer is specified for an object of (possibly
cv-qualified) class type (or array thereof), or the initializer has
the form
(),
the object is initialized as specified in [dcl.init].
When an array of class objects is initialized
(either explicitly or implicitly) and the elements are initialized by constructor,
the constructor shall be called for each element of the array,
following the subscript order; see [dcl.array].