Note that this doesn't necessarily mean that the instance is immutable.
Other code holding a reference to the underlying
Array can still modify it,
and the reference can be obtained with a
Returns a new Array by appending the elements of
a to the elements of
This operation does not modify
a is the empty Array
, a copy of
this Array is returned.
The length of the returned Array is equal to the sum of
null, the result is unspecified.