The View hierarchy of classes is reorganized to include new
classes with member functions moved and renamed, to solve
defects in the original design:
OpenView accumulates raw state and tx changes and
can be applied to the base. ApplyView accumulates changes
for a single transaction, including metadata, and can be
applied to an OpenView. The Sandbox allows changes with
the option to apply or throw them out. The PaymentSandbox
provides a sandbox with account credit deferral.
Call sites are changed to use the class appropriate for
the task.
Member functions and free functions on Ledger and LedgerEntrySet are
rewritten in terms of new abstract interfaces `BasicView` and `View`,
representing the set of non-decomposable primitives necessary to read
and write state map items in a ledger, and to overlay a discardable
view onto a Ledger that can calculate metadata during transaction
processing. const-correctness is enforced through the parameter and
return types.
The MetaView now supports multi-level stacking: A MetaView can be
stacked on top of either a Ledger or another MetaView, up to any
number of levels.
The getSLEi member function is removed. The CachedView wrapper
replaces it, wrapping a View such that any function called with a
CachedView will go through the SLECache.
* Add BasicView, View, CachedView
* Rename LedgerEntrySet to MetaView
* Factor out free functions
* Consolidate free functions in ViewAPI
* Remove unused class members and free functions
