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Package overview: net.sf.saxon.ma.parray
This package contains an implementation of persistent immutable arrays.
("Persistent" seems to have acquired a new meaning. It no longer refers to
values that outlive the execution of the program that created them, but now refers
to data structures where modification actions leave the existing value unchanged.)
The first version of this package (released with Saxon 9.9.0.1) took code from
the PCollections library at https://github.com/hrldcpr/pcollections. In 9.9.1.1 this has
been replaced by a home-brew implementation written entirely by Saxonica.
The implementation uses a simple binary tree, in which the left-hand half of the
array is in one subtree, and the right-hand half in the other. The tree is kept
balanced as necessary. There are two special-case implementations for empty and
singleton trees.