It also gives different results if options has a default value or a
default proc.
If the default value is expensive to produce, using the block version
of Hash#fetch may be better for performance, as then it will only
produce the expensive value if the options hash doesn't contain the
option.
It's generally considered bad style to modify arguments passed into a
method unless that is the purpose of the method itself. Using:
options.reverse_merge!(:length => 30)
or
options[:length] ||= 30
modifies the options hash, and that's a bad idea IMO.
Jeremy