lib.rs

// Copyright 2017-2019 Parity Technologies (UK) Ltd.
// This file is part of Substrate.

// Substrate is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Substrate is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.

//! # Balances Module
//!
//! The Balances module provides functionality for handling accounts and balances.
//! To use it in your runtime, you need to implement the [`balances::Trait`](./trait.Trait.html).
//! Dispatchable functions are documented as part of the [`Call`](./enum.Call.html) enum.
//!
//! ## 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.
//! - **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 balance is set
//! to zero.
//! - **Free Balance:** The portion of a balance that is not reserved. The free balance is the only balance that matters
//! for most operations. When this balance falls below the existential deposit, most functionality of the account is
//! removed. When both it and the reserved balance are deleted, then the account is said to be dead.
//! - **Reserved Balance:** Reserved balance still belongs to the account holder, but is suspended. Reserved balance
//! can still be slashed, but only after all of free balance has been slashed. If the reserved balance falls below the
//! existential deposit then it and any related functionality will be deleted. When both it and the free balance are
//! deleted, then the account is said to be dead.
//! - **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 must be handled.
//! - **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".
//! - **Vesting:** Similar to a lock, this is another, but independent, liquidity restriction that reduces linearly
//! over time.
//!
//! ### 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`](../srml_support/traits/trait.Currency.html): Functions for dealing with a
//! fungible assets system.
//! - [`ReservableCurrency`](../srml_support/traits/trait.ReservableCurrency.html):
//! Functions for dealing with assets that can be reserved from an account.
//! - [`LockableCurrency`](../srml_support/traits/trait.LockableCurrency.html): Functions for
//! dealing with accounts that allow liquidity restrictions.
//! - [`Imbalance`](../srml_support/traits/trait.Imbalance.html): 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).
//! - [`MakePayment`](../srml_support/traits/trait.MakePayment.html): Simple trait designed
//! for hooking into a transaction payment.
//! - [`IsDeadAccount`](../srml_system/trait.IsDeadAccount.html): 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.
//!
//! See the [`Call`](./enum.Call.html) enum and its associated variants for details of each function.
//!
//! ### Public Functions
//!
//! - `vesting_balance` - Get the amount that is currently being vested and cannot be transferred out of this account.
//!
//! See the [`Module`](./struct.Module.html) struct for details of publicly available functions.
//!
//! ## Usage
//!
//! The following examples show how to use the Balances module in your custom module.
//!
//! ### Example from the SRML
//!
//! The Contract module uses the `Currency` trait to handle gas.
//!
//! [(lib.rs)](https://github.com/paritytech/substrate/blob/master/srml/contract/src/lib.rs):
//!
//! ```rust,ignore
//! use srml_support::traits::Currency
//!
//! pub type BalanceOf<T> = <<T as Trait>::Currency as Currency<<T as system::Trait>::AccountId>>::Balance;
//! pub type NegativeImbalanceOf<T> = <<T as Trait>::Currency as Currency<<T as system::Trait>::AccountId>>::NegativeImbalance;
//!```
//!
//! [(gas.rs)](https://github.com/paritytech/substrate/blob/master/srml/contract/src/gas.rs):
//!
//! ```rust,ignore
//! use srml_support::traits::Currency
//!
//! pub fn refund_unused_gas<T: Trait>(
//! 	transactor: &T::AccountId,
//! 	gas_meter: GasMeter<T>,
//! 	imbalance: NegativeImbalanceOf<T>,
//! ) {
//! 	let gas_spent = gas_meter.spent();
//! 	let gas_left = gas_meter.gas_left();
//!
//! 	// Increase total spent gas.
//! 	<GasSpent<T>>::mutate(|block_gas_spent| *block_gas_spent += gas_spent);
//!
//! 	// Refund gas left by the price it was bought at.
//! 	let refund = <T::Gas as As<BalanceOf<T>>>::as_(gas_left) * gas_meter.gas_price;
//! 	let refund_imbalance = T::Currency::deposit_creating(transactor, refund);
//! 	if let Ok(imbalance) = imbalance.offset(refund_imbalance) {
//! 		T::GasPayment::on_unbalanced(imbalance);
//! 	}
//! }
//! ```
//!
//! ## Genesis config
//!
//! The Balances module depends on the genesis configuration. See the [`GenesisConfig`](./struct.GenesisConfig.html)
//! struct for a list of attributes that can be provided.
//!
//! ## Related Modules
//!
//! - [`system`](../srml_system/index.html)
//! - [`srml_support`](../srml_support/index.html)

#![cfg_attr(not(feature = "std"), no_std)]

use rstd::prelude::*;
use rstd::{cmp, result};
use parity_codec::{Codec, Encode, Decode};
use srml_support::{StorageValue, StorageMap, Parameter, decl_event, decl_storage, decl_module};
use srml_support::traits::{
	UpdateBalanceOutcome, Currency, OnFreeBalanceZero, MakePayment, OnUnbalanced,
	WithdrawReason, WithdrawReasons, LockIdentifier, LockableCurrency, ExistenceRequirement,
	Imbalance, SignedImbalance, ReservableCurrency
};
use srml_support::dispatch::Result;
use primitives::traits::{
	Zero, SimpleArithmetic, As, StaticLookup, Member, CheckedAdd, CheckedSub,
	MaybeSerializeDebug, Saturating
};
use system::{IsDeadAccount, OnNewAccount, ensure_signed};

mod mock;
mod tests;

pub use self::imbalances::{PositiveImbalance, NegativeImbalance};

pub trait Subtrait<I: Instance = DefaultInstance>: system::Trait {
	/// The balance of an account.
	type Balance: Parameter + Member + SimpleArithmetic + Codec + Default + Copy + As<usize> + As<u64> + MaybeSerializeDebug;

	/// A function that is invoked when the free-balance has fallen below the existential deposit and
	/// has been reduced to zero.
	///
	/// Gives a chance to clean up resources associated with the given account.
	type OnFreeBalanceZero: OnFreeBalanceZero<Self::AccountId>;

	/// Handler for when a new account is created.
	type OnNewAccount: OnNewAccount<Self::AccountId>;
}

pub trait Trait<I: Instance = DefaultInstance>: system::Trait {
	/// The balance of an account.
	type Balance: Parameter + Member + SimpleArithmetic + Codec + Default + Copy + As<usize> + As<u64> + MaybeSerializeDebug;

	/// A function that is invoked when the free-balance has fallen below the existential deposit and
	/// has been reduced to zero.
	///
	/// Gives a chance to clean up resources associated with the given account.
	type OnFreeBalanceZero: OnFreeBalanceZero<Self::AccountId>;

	/// Handler for when a new account is created.
	type OnNewAccount: OnNewAccount<Self::AccountId>;

	/// Handler for the unbalanced reduction when taking transaction fees.
	type TransactionPayment: OnUnbalanced<NegativeImbalance<Self, I>>;

	/// Handler for the unbalanced reduction when taking fees associated with balance
	/// transfer (which may also include account creation).
	type TransferPayment: OnUnbalanced<NegativeImbalance<Self, I>>;