Example starknet contract that contains a list of entries. (This has been tricky, as lists by keys are not native in cairo/starknet)
$ ./stored_list.sh
Before you run it, this will:
- Run the python tests for the contract
- Looking for a unknown key of a unknown user
- Test the return of -1
- Receive the count of keys for an unknown user
- Adding two keys for a user
- Replacing a key at an index
- Removing the last entry
- Finding the index of a key with several keys added
- Removing a key at a position
- Running cairo code really takes alot of time. Using Python test code to make sure that the contract works before testing it in the live network, gives a great advantage. However, unlike all other pieces of code, the test system is requiring exactly python 3.7 - not python 3.9! So you need to make sure that the venv is of the exact version.
- Negative integers can be used in cairo code but are treated in the API as number overflows.
-1would be - Natively cairo doesn't help to store arrays or sets of data for a given item, but by using a hash of a key location we can use a similar structure in a contract.
- Instead of removing data it is enough to just reduce the size. In blockchain the history is preserved and the old entries won't go away. So we just keep them but the reader is not directly made aware of.
- There is a relatively good pattern of
get_<X>_countfor the length,get_<X>_atusepush_<X>andpop_<X>to add/remove entries.set_<X>_atcan be effective to remove/add a key in one operation.get_<X>_indexis an easy operation that is helpful for other operations. - Operations like
remove_<X>_atorremove_keyare a lot more complex to execute (ether cost).