t growable list, as returned by <code>new List()</code> or <code>[]</code>, keeps
an internal buffer, and grows that buffer when necessary. This guarantees
that a sequence of <a href="dart-core/List/add.html">add</a> operations will each execute in amortized constant
time. Setting the length directly may take time proportional to the new
length, and may change the internal capacity so that a following add
operation will need to immediately increase the buffer capacity.
Other list implementations may have di