Holds the values from 1 to N with as little storage interaction as possible
If Mapper[i] = i, then it stores nothing, i.e. “0”
If Mapper[i] is equal to another value, then it stores the value
Very widely used mapper, that manages the users of a smart contract.
It holds a bi-directional map, from addresses to ids and viceversa.
This is so we can easily iterate over all users, using their ids.
Also holds the user count in sync. This is also necessary for iteration.
Manages a list of items of the same type.
Saves each of the items under a separate key in storage.
To produce each individual key, it concatenates the main key with a serialized 4-byte index.
Indexes start from 1, instead of 0. (We avoid 0-value indexes to prevent confusion between an uninitialized variable and zero.)
It also stores the count separately, at what would be index 0.
The count is always kept in sync automatically.
A non-iterable whitelist mapper.
Very efficient for storing a whitelist, as each item requires only one storage key.
If you need to iterate over the keys, use UnorderedSetMapper or SetMapper instead.