breve allows simulations and individual objects within simulations to be archived into human-readable XML files, and then later extracted. The XML archive/dearchive process applies both to saving simulation objects to files and to sending objects over a network. Both techniques require object encoding and decoding, and the discussion in this chapter applies to both.
This chapter first describes how individual objects can be archived and dearchived (the section called “Saving and Loading Individual Objects”) and then how entire simulations can be archived and dearchived (the section called “Saving and Loading the Entire State of a Simulation”). Though this simulation discusses archiving to and from files, the same techniques discussed in this section are used for networking.
Important note: archiving and dearchiving is currently only supported in the steve language frontend, not the Python language frontend. Support for Python archiving and dearchiving is forthcoming in a future breve release.
During dearchiving, the following steve language types are
automatically saved and restored: int, float,
string, list, hash, data. The pointer type is not automatically restored.
The object type is restored only if the
other object was dearchived from the same archive. If an object to be
archived contains only the types which are automatically saved and
restored, no further action is required to prepare the objects for
saving and loading.
pointer or object types,
data will need to be carefully encoded and decoded. The special methods
archive and dearchive are called automatically during archiving and
dearchiving respectively. The "archive" method should be implemented, if
necessary, to prepare a user object for archiving. The "dearchive" method
should be implemented, if necessary, after an object has been archived to
prepare it for being loaded into a simulation.
For many users, these methods are not required and should not be
implemented. If they are implemented, however, they must return 1 to indicate success and unless
the methods are specifically intended to override superclass behaviors,
they must call the superclass
implementation. In most cases, it is desirable to return
the same value as the superclass implementation so that errors are
handled correctly. Example archive and
dearchive methods are shown below. These
methods do no special preparation for archiving and dearchiving, but
instead fulfill the requirements listed above and print a message.
+ to archive:
print "Archiving $self...".
return (super archive).
+ to dearchive:
print "Dearchiving $self...".
return (super archive).