Crate pallet_balances[−][src]

Balances Module

The Balances module provides functionality for handling accounts and balances.

Overview

The Balances module provides functions for:

Getting and setting free balances.
Retrieving total, reserved and unreserved balances.
Repatriating a reserved balance to a beneficiary account that exists.
Transferring a balance between accounts (when not reserved).
Slashing an account balance.
Account creation and removal.
Managing total issuance.
Setting and managing locks.

Terminology

Existential Deposit: The minimum balance required to create or keep an account open. This prevents “dust accounts” from filling storage. When the free plus the reserved balance (i.e. the total balance) fall below this, then the account is said to be dead; and it loses its functionality as well as any prior history and all information on it is removed from the chain’s state. No account should ever have a total balance that is strictly between 0 and the existential deposit (exclusive). If this ever happens, it indicates either a bug in this module or an erroneous raw mutation of storage.
Total Issuance: The total number of units in existence in a system.
Reaping an account: The act of removing an account by resetting its nonce. Happens after its total balance has become zero (or, strictly speaking, less than the Existential Deposit).
Free Balance: The portion of a balance that is not reserved. The free balance is the only balance that matters for most operations.
Reserved Balance: Reserved balance still belongs to the account holder, but is suspended. Reserved balance can still be slashed, but only after all the free balance has been slashed.
Imbalance: A condition when some funds were credited or debited without equal and opposite accounting (i.e. a difference between total issuance and account balances). Functions that result in an imbalance will return an object of the Imbalance trait that can be managed within your runtime logic. (If an imbalance is simply dropped, it should automatically maintain any book-keeping such as total issuance.)
Lock: A freeze on a specified amount of an account’s free balance until a specified block number. Multiple locks always operate over the same funds, so they “overlay” rather than “stack”.

Implementations

The Balances module provides implementations for the following traits. If these traits provide the functionality that you need, then you can avoid coupling with the Balances module.

Currency: Functions for dealing with a fungible assets system.
ReservableCurrency: Functions for dealing with assets that can be reserved from an account.
LockableCurrency: Functions for dealing with accounts that allow liquidity restrictions.
Imbalance: Functions for handling imbalances between total issuance in the system and account balances. Must be used when a function creates new funds (e.g. a reward) or destroys some funds (e.g. a system fee).
IsDeadAccount: Determiner to say whether a given account is unused.

Interface

Dispatchable Functions

transfer - Transfer some liquid free balance to another account.
set_balance - Set the balances of a given account. The origin of this call must be root.

Usage

The following examples show how to use the Balances module in your custom module.

Examples from the FRAME

The Contract module uses the Currency trait to handle gas payment, and its types inherit from Currency:

use frame_support::traits::Currency;

pub type BalanceOf<T> = <<T as Trait>::Currency as Currency<<T as frame_system::Trait>::AccountId>>::Balance;
pub type NegativeImbalanceOf<T> = <<T as Trait>::Currency as Currency<<T as frame_system::Trait>::AccountId>>::NegativeImbalance;

The Staking module uses the LockableCurrency trait to lock a stash account’s funds:

use frame_support::traits::{WithdrawReasons, LockableCurrency};
use sp_runtime::traits::Bounded;
pub trait Trait: frame_system::Trait {
	type Currency: LockableCurrency<Self::AccountId, Moment=Self::BlockNumber>;
}

fn update_ledger<T: Trait>(
	controller: &T::AccountId,
	ledger: &StakingLedger<T>
) {
	T::Currency::set_lock(
		STAKING_ID,
		&ledger.stash,
		ledger.total,
		WithdrawReasons::all()
	);
	// <Ledger<T>>::insert(controller, ledger); // Commented out as we don't have access to Staking's storage here.
}

Genesis config

The Balances module depends on the GenesisConfig.

Assumptions

Total issued balanced of all accounts should be less than Trait::Balance::max_value().

Structs

Account	The balance of an account.
AccountData	All balance information for an account.
BalanceLock	A single lock on a balance. There can be many of these on an account and they “overlap”, so the same balance is frozen by multiple locks.
DefaultInstance	Default module instance
GenesisConfig	Genesis config for the module, allow to build genesis storage.
Instance0	Module instance
Instance1	Module instance
Instance2	Module instance
Instance3	Module instance
Instance4	Module instance
Instance5	Module instance
Instance6	Module instance
Instance7	Module instance
Instance8	Module instance
Instance9	Module instance
Instance10	Module instance
Instance11	Module instance
Instance12	Module instance
Instance13	Module instance
Instance14	Module instance
Instance15	Module instance
Locks	Any liquidity locks on some account balances. NOTE: Should only be accessed when setting, changing and freeing a lock.
Module
NegativeImbalance	Opaque, move-only struct with private fields that serves as a token denoting that funds have been destroyed without any equal and opposite accounting.
PositiveImbalance	Opaque, move-only struct with private fields that serves as a token denoting that funds have been created without any equal and opposite accounting.
TotalIssuance	The total units issued in the system.

Enums

Call	Dispatchable calls.
Error
RawEvent	Events for this module.
Reasons	Simplified reasons for withdrawing balance.

Traits

Subtrait
Trait
WeightInfo

Type Definitions

Event

RawEvent specialized for the configuration Trait