Are there any sid3-effects of using mappings in structs?

Question

I have a question for any solidity expert out there. Is there any downside/security risk to storing mappings inside structs? I'm aware that deleting the struct won't delete the mapping as it's stored as a keccak256 of the mapping name and key rather than inside the struct itself.

I also aware that with ethers the mapping won't be returned as the evm doesnt store the mapping in the struct so it doesnt know where to find it except a separate getter function is created for it

Sergey Ilin · Answer

In addition to your points:

1 - A struct containing mapping can't be stored in a memory variable and will cause Type struct XXX is only valid in storage because it contains a (nested) mapping.;

2 - All keys in a mapping are always initialized with value 0x0. For that reason, 0x0 in the logic should be reserved for uninitialized values. Otherwise, there is no way to differentiate a value that was set to 0x0 and uninitialized value;

3 - There is now way to list all set key values in a mapping nor their count. If there is a need for that, then they need to be stored separately. OpenZepplin provides few class for extending the mapping, for example EnumerableMap.

Are there any sid3-effects of using mappings in structs?

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