The term "parent" as it has previously been used in this module is
confusing, because it referred not to the actual parent of a leaf note,
but to the *sibling* of the leaf's future parent. "Ommer" is a
gender-neutral term for the sibling of a parent, so it is ideal
for use in this context.
For some applications, it is not necessary to include the
full range of witnessing and checkpointing operations. The
Frontier trait captures the minimal operations required:
appending leaves to the tree and constructing the root
of the tree by hashing against empty nodes.
In this commit:
* TreeHasher is replaced by the Hashable trait. Hashable is
modified to use level information in the construction of
the hash, and a convenience method is provided for obtaining
the empty node at a given level.
* The pop_checkpoint method is removed from the `Tree` interface.
Instead, a maximum number of checkpoints is established at tree
construction time and then the oldest checkpoints are automatically
dropped when adding new checkpoints once that number is reached.
* The `witness` method implementation in the sample tree
is modified to ignore duplicate calls.
* Property testing functiona are modified to abstract over
the type of hashable data.
Kris Nuttycombe
Kris Nuttycombe
Kris Nuttycombe
str4d
Sean Bowe