Hey guys,
Does anyone have experience using the command
pattern<http://en.wikipedia.org/wiki/Command_pattern>?
I’m looking for a few things that this pattern seems to help with.
-
Undo/redo (preferable multi-level and persistent)
-
Action logging (what the user has done, in which order, and where things
went wrong using which arguments)
- Distribution of commands via a network (serialisation, asynchronous
execution)
I took a whack at it and found it rather straightforward to make a
scripting-language out of it.
The Command Pattern <https://gist.github.com/mottosso/f5722c4afd1b0791c4d3>
There’s an example run at the bottom, but the ‘gist’ of it is this:
______________________________________________________
| |
| Command Pattern - Demonstration |
| Author: Marcus Ottosson <[email protected]> |
|______________________________________________________|
* Available commands
cls
create
data
delete
exit
help
history
redo
undo
update
verbosity
command> create key value
command> create age 5
command> create length 1.57
command> data
age=5
length=1.57
key=value
command> undo
command> redo
command> help update
Update existing value in DATASTORE
Args:
key: Identifier for value
value: Value for identifier
Precondition:
`key` must already exist
Example:
command> update age 5
The main questions are about two aspects of it’s design:
*History is stored as class attributes*
Which means that commands add themselves to history, which wouldn’t work
too great if they are accessed from separate threads.
*History is stored as Python objects, as opposed to simple strings*
Which means that history would be tricky to serialise and persist on disk
or across a network.
Thoughts?
Best,
Marcus
--
*Marcus Ottosson*
[email protected]
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