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rustblockchainsmartcontractsnearprotocol

The value of an instance variable on NEAR - shared among every client? Or unique per client?

Suppose I have this simple code in a smart contract:

#[near_bindgen]
pub struct A {
    pub var1: AccountId,
    pub var2: Balance,
    pub my_map: TreeMap<String, (u128, u128, u128)>,
}

#[near_bindgen]
impl A {
    #[init]
    pub fn init() -> Self {
        let _my_map: TreeMap<String, (u128, u128, u128)> = TreeMap::new(b"t");
        Self {
          //...other fields
          my_map: _my_map
        }
    }

    //!!!
    // will this work properly for each client at all?
    //
    pub fn my_method1(&mut self) {

        // !! instance variable !!
        if !self.my_map.contains_key("some_key") {
            self.my_map.insert(&"aaa", &(1, 2, 3));
        } else {
           // already exists, error!
        }
    }
}

In the ordinary environment this Rust code would everyone to have his own instance of A and with its unique values of the fields. Correct?

Do I understand correctly, that in NEAR everyone -- client -- would have the same instance of A?

Namely, the instance variable A.my_map would contain the same data for every client of a smart contract where this code may be used?

How about A.var1 and A.var2 then?

Solution

  • A smart contract persists state between invocations. In your example, my_map and other variables will be the same every time anyone calls my_method1 in your contract.

    This state is persistent within the network your smart contract is deployed, meaning - for testnet and mainnet it’ll be separate.

    If you wish, for example, to manage separate state for different callers, check out this example: https://github.com/near-examples/rust-status-message/blob/master/src/lib.rs It uses a mapping between caller’s account ID and data related to it.