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Complex State and Maps

Of course, for most non-trivial examples, additional data will need to be stored. You can serialise larger JSON data structures, and use key-value lookups to access this data.

In CW20, the mapping of addresses to their CW20 balance is achieved through just such a map:

pub const BALANCES: Map<&Addr, Uint128> = Map::new("balance");

The code for this can be found here.

You can see how it is interacted with in here. The relevant snippet is:

let rcpt_addr = deps.api.addr_validate( & recipient) ?;
& rcpt_addr,
| balance: Option<Uint128> | -> StdResult<_ > { Ok(balance.unwrap_or_default() + amount) },
) ?;

There's a bit going on here, so let's unpack it.

  1. is passed in. This is from the contract context. deps is similar to the ctx you will have seen in the Cosmos SDK.
  2. &rcpt_addr is a borrowed reference to the validated recipient address - it is valid, or the let statement would have errored. This is the key half of the key/value pair.
  3. The third statement is a lambda (anonymous function) returning StdResult that does some computation based on the current value of balance, where balance is the value half, and &rcpt_addr is the key.

More sophisticated contracts, such as CW1155, allow for the creation and management of multiple coins.

For more advanced usage, indexing and more, check out: