Not only is the faster than a classical iterator (though still not as
fast as a while loop), but it also offers the choice of characters
or code points.
The maintenance burden is not worth the advantages it provides in
limited situations.
Moreover, if other decoders are to be implemented, most multi-byte
schemes would not be able to support a functional interface of similar
simplicity, and single-byte schemes wouldn't benefit much
The Intl tests avoided one mission user-function calls by doing a simple
loop, something unlikely to be used in real-world situations; wrapping
the test in a generator adds the overhead one would expect to have,
making the pure PHP implementation much more competitive
J. King