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Zilliqa
New builtin for field map garbage collection
Some contracts tend to accumulate lots of nested empty maps and when the semantics of the contract permits we should have a mechanism to clean the empty maps. @vaivaswatha has suggested to implement this as a new builtin because it's easier to do this at the C++ level.
Example:
A map like this
{
"key1" -> {"key1a" -> 42}
"key2" -> {}
"key3" -> {}
...
"key42" -> {}
}
often times can be simplified to
{
"key1" -> {"key1a" -> 42}
}
A common scenario is when in a nested map, all keys of a nested map are deleted (and we have an empty map), but the corresponding key in the outer map (that now holds an empty inner map as its value) lives on.
A builtin can be provided to prune such keys in an outer map that have empty map values.
Implementation: It looks to me that the best way to do this is to have a direct call, via IPC, to the blockchain code that will scan the leveldb database and perform this operation.
Edit: This comment turned out to be redundant given @anton-trunov 's update to the Issue description. I'll let it stay on though.
