Creating Accounts

You might want to create an account from a contract for many reasons. One example: You want to progressively onboard users, hiding the whole concept of NEAR from them at the beginning, and automatically create accounts for them (these could be sub-accounts of your main contract, such as user123.some-cool-game.near).

Since an account with no balance is almost unusable, you probably want to combine this with the token transfer from the last page. You will also need to give the account an access key. Here's a way do it:

Promise::new("subaccount.example.near".parse().unwrap())
    .create_account()
    .add_full_access_key(env::signer_account_pk())
    .transfer(250_000_000_000_000_000_000_000); // 2.5e23yN, 0.25N

In the context of a full contract:

use near_sdk::{env, near_bindgen, AccountId, Balance, Promise};

const INITIAL_BALANCE: Balance = 250_000_000_000_000_000_000_000; // 2.5e23yN, 0.25N

#[near_bindgen]
pub struct Contract {}

#[near_bindgen]
impl Contract {
    #[private]
    pub fn create_subaccount(prefix: AccountId) -> Promise {
        let subaccount_id = AccountId::new_unchecked(
          format!("{}.{}", prefix, env::current_account_id())
        );
        Promise::new(subaccount_id)
            .create_account()
            .add_full_access_key(env::signer_account_pk())
            .transfer(INITIAL_BALANCE)
    }
}

Things to note:

• add_full_access_key – This example passes in the public key of the human or app that signed the original transaction that resulted in this function call (signer_account_pk). You could also use add_access_key to add a Function Call access key that only permits the account to make calls to a predefined set of contract functions.
• #[private] – if you have a function that spends your contract's funds, you probably want to protect it in some way. This example does so with a perhaps-too-simple #[private] macro.
• INITIAL_BALANCE uses the Balance type from near-sdk-rs. Today this is a simple alias for u128, but in the future may be expanded to have additional functionality, similar to recent changes to the Gas type.