Implemented lens-like ZRef focusing on state components #3257
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This is a proposal for more general than
foldtransformer forZRefnamedfocusFoldwith lens-like interface.Such a transformer can focus mutable access on individual components of product types, such as case classes and collections.
Changes overview:
focusFold, which can analyze old read value during an update.ZRefnamedFocusedwhich has worse performance in general than previousDerived.Derivedrenamed toMappedand now extendsFocusedto reduce code repetition