While command classes define how the client should filter arguments or
parse responses, key prefixing depends on the actual command signature
as defined by Redis so it really is something that should be handled
separately as the norm.
Developers can define new handlers or override existing ones, but they
can still define the key prefixing logic inside their command classes
by implementing Predis\Command\PrefixableCommandInterface: the key
prefix processor will just use that by overriding any defined handler.
Actually this was already the case for certain commands, but some of them
was left unguarded for such cases. This commit also fixes#109.
The behaviour of silently skipping key prefixing when a command has no
arguments may change in the future so we added explicit tests as guards
for future changes. Predis\Command\Processor\KeyPrefixProcessor will
continue to skip key prefixing on empty arguments, regardless.
The reason for this change is to support the upcoming redis-cluster since
it has different behaviors compared to the client-side cluster implementation
provided by Predis. For example redis-cluster will not support key tags or
certain operations currently available with our client-side implementation.
Daniele Alessandri