Simple State

State is where the smart contract works with saving and retrieving data. You can think of it much like a database interaction layer in a traditional application.

The most simple way of writing state is by writing a single item.

For example, in the cw20-base contract, TokenInfo is written when the contract is instantiated.

First, a TokenInfo type is declared in state.rs:

#[derive(Serialize, Deserialize, Clone, PartialEq, JsonSchema, Debug)]
#[serde(rename_all = "snake_case")]
pub struct TokenInfo {
  pub name: String,
  pub symbol: String,
  pub decimals: u8,
  pub total_supply: Uint128,
  pub mint: Option<MinterData>,
}

Then the storage is initialized:

pub const TOKEN_INFO: Item<TokenInfo> = Item::new("token_info");

In the contract, we see in the instantiate function how data can be saved to this:

let data = TokenInfo {
name: msg.name,
symbol: msg.symbol,
decimals: msg.decimals,
total_supply,
mint,
};
TOKEN_INFO.save(deps.storage, & data) ?;

Here's the code context.