chef

Chef::ChefFS::FileSystem::BaseFSObject#compare_to

Override this if you have a special comparison algorithm that can tell
you whether this entry is the same as another--either a quicker or a
more reliable one.  Callers will use this to decide whether to upload,
download or diff an object.

You should not override this if you're going to do the standard
+self.read == other.read+.  If you return +nil+, the caller will call
+other.compare_to(you)+ instead.  Give them a chance :)

==== Parameters

* +other+ - the entry to compare to

==== Returns

* +[ are_same, value, other_value ]+
  +are_same+ may be +true+, +false+ or +nil+ (which means "don't know").
  +value+ and +other_value+ must either be the text of +self+ or +other+,
  +:none+ (if the entry does not exist or has no value) or +nil+ if the
  value was not retrieved.
* +nil+ if a definitive answer cannot be had and nothing was retrieved.

==== Example

    are_same, value, other_value = entry.compare_to(other)
    if are_same.nil?
      are_same, other_value, value = other.compare_to(entry)
    end
    if are_same.nil?
      value = entry.read if value.nil?
      other_value = entry.read if other_value.nil?
      are_same = (value == other_value)
    end

Source | Google | Stack overflow