lib.rs

		Ok(())
	}

	// Transfer some free balance from `transactor` to `dest`, respecting existence requirements.
	// Is a no-op if value to be transferred is zero or the `transactor` is the same as `dest`.
	fn transfer(
		transactor: &T::AccountId,
		dest: &T::AccountId,
		value: Self::Balance,
		existence_requirement: ExistenceRequirement,
	) -> DispatchResult {
		if value.is_zero() || transactor == dest { return Ok(()) }

		let old_from_account = Self::account(transactor);
		let mut from_account = old_from_account.clone();
		let old_to_account = Self::account(dest);
		let mut to_account = old_to_account.clone();

		let would_create = to_account.total().is_zero();
		let fee = if would_create { T::CreationFee::get() } else { Zero::zero() };
		let liability = value.checked_add(&fee).ok_or(Error::<T, I>::Overflow)?;

		from_account.free = from_account.free.checked_sub(&liability)
			.ok_or(Error::<T, I>::InsufficientBalance)?;

		// NOTE: total stake being stored in the same type means that this could never overflow
		// but better to be safe than sorry.
		to_account.free = to_account.free.checked_add(&value).ok_or(Error::<T, I>::Overflow)?;

		let ed = T::ExistentialDeposit::get();
		ensure!(to_account.free >= ed, Error::<T, I>::ExistentialDeposit);

		Self::ensure_can_withdraw(
			transactor,
			value,
			WithdrawReason::Transfer.into(),
			from_account.free,
		)?;

		let allow_death = existence_requirement == ExistenceRequirement::AllowDeath;
		ensure!(allow_death || from_account.free >= ed, Error::<T, I>::KeepAlive);

		Self::set_account(transactor, &from_account, &old_from_account);

		// Take action on the set_account call.
		// This will emit events that _resulted_ from the transfer.
		Self::set_account(dest, &to_account, &old_to_account);

		// Emit transfer event.
		Self::deposit_event(RawEvent::Transfer(transactor.clone(), dest.clone(), value, fee));

		T::TransferPayment::on_unbalanced(NegativeImbalance::new(fee));

		Ok(())
	}

	// Withdraw some free balance from an account, respecting existence requirements.
	// Is a no-op if value to be withdrawn is zero.
	fn withdraw(
		who: &T::AccountId,
		value: Self::Balance,
		reasons: WithdrawReasons,
		liveness: ExistenceRequirement,
	) -> result::Result<Self::NegativeImbalance, DispatchError> {
		if value.is_zero() { return Ok(NegativeImbalance::zero()); }

		let old_account = Self::account(who);
		let mut account = old_account.clone();
		if let Some(new_free_account) = account.free.checked_sub(&value) {
			// if we need to keep the account alive...
			if liveness == ExistenceRequirement::KeepAlive
				// ...and it would be dead afterwards...
				&& new_free_account < T::ExistentialDeposit::get()
				// ...yet is was alive before
				&& account.free >= T::ExistentialDeposit::get()
			{
				Err(Error::<T, I>::KeepAlive)?
			}
			Self::ensure_can_withdraw(who, value, reasons, new_free_account)?;
			account.free = new_free_account;
			Self::set_account(who, &account, &old_account);
			Ok(NegativeImbalance::new(value))
		} else {
			Err(Error::<T, I>::InsufficientBalance)?
		}
	}

	/// Slash a target account `who`, returning the negative imbalance created and any left over
	/// amount that could not be slashed.
	///
	/// Is a no-op if `value` to be slashed is zero.
	///
	/// NOTE: `slash()` prefers free balance, but assumes that reserve balance can be drawn
	/// from in extreme circumstances. `can_slash()` should be used prior to `slash()` to avoid having
	/// to draw from reserved funds, however we err on the side of punishment if things are inconsistent
	/// or `can_slash` wasn't used appropriately.
	fn slash(
		who: &T::AccountId,
		value: Self::Balance
	) -> (Self::NegativeImbalance, Self::Balance) {
		if value.is_zero() { return (NegativeImbalance::zero(), Zero::zero()) }

		let old_account = Self::account(who);
		let mut account = old_account.clone();

		let free_slash = cmp::min(account.free, value);
		account.free -= free_slash;

		let remaining_slash = value - free_slash;
		let result = if !remaining_slash.is_zero() {
			let reserved_slash = cmp::min(account.reserved, remaining_slash);
			account.reserved -= reserved_slash;
			(NegativeImbalance::new(free_slash + reserved_slash), remaining_slash - reserved_slash)
		} else {
			(NegativeImbalance::new(value), Zero::zero())
		};
		Self::set_account(who, &account, &old_account);
		result
	}

	/// Deposit some `value` into the free balance of an existing target account `who`.
	///
	/// Is a no-op if the `value` to be deposited is zero.
	fn deposit_into_existing(
		who: &T::AccountId,
		value: Self::Balance
	) -> result::Result<Self::PositiveImbalance, DispatchError> {
		if value.is_zero() { return Ok(PositiveImbalance::zero()) }

		let old_account = Self::account(who);
		let mut account = old_account.clone();
		ensure!(!account.total().is_zero(), Error::<T, I>::DeadAccount);
		account.free = account.free.checked_add(&value).ok_or(Error::<T, I>::Overflow)?;

		Self::set_account(who, &account, &old_account);
		Ok(PositiveImbalance::new(value))
	}

	/// Deposit some `value` into the free balance of `who`, possibly creating a new account.
	///
	/// This function is a no-op if:
	/// - the `value` to be deposited is zero; or
	/// - if the `value` to be deposited is less than the ED and the account does not yet exist; or
	/// - `value` is so large it would cause the balance of `who` to overflow.
	fn deposit_creating(
		who: &T::AccountId,
		value: Self::Balance,
	) -> Self::PositiveImbalance {
		if value.is_zero() { return Self::PositiveImbalance::zero() }

		let old_account = Self::account(who);
		let mut account = old_account.clone();
		let ed = T::ExistentialDeposit::get();

		// bail if not yet created and this operation wouldn't be enough to create it.
		if value < ed && account.total().is_zero() { return Self::PositiveImbalance::zero() }

		// defensive only: overflow should never happen, however in case it does, then this
		// operation is a no-op.
		account.free = match account.free.checked_add(&value) {
			Some(f) => f,
			None => return Self::PositiveImbalance::zero(),
		};

		Self::set_account(who, &account, &old_account);

		PositiveImbalance::new(value)
	}

	/// Force the new free balance of a target account `who` to some new value `balance`.
	fn make_free_balance_be(who: &T::AccountId, value: Self::Balance) -> (
		SignedImbalance<Self::Balance, Self::PositiveImbalance>,
		UpdateBalanceOutcome
	) {
		let old_account = Self::account(who);
		let mut account = old_account.clone();

		if value < T::ExistentialDeposit::get() && account.free.is_zero() {
			// If we're attempting to set an existing account to less than ED, then
			// bypass the entire operation. It's a no-op if you follow it through, but
			// since this is an instance where we might account for a negative imbalance
			// (in the dust cleaner of set_account) before we account for its actual
			// equal and opposite cause (returned as an Imbalance), then in the
			// instance that there's no other accounts on the system at all, we might
			// underflow the issuance and our arithmetic will be off.
			return (
				SignedImbalance::Positive(Self::PositiveImbalance::zero()),
				UpdateBalanceOutcome::AccountKilled,
			)
		}
		let imbalance = if account.free <= value {
			SignedImbalance::Positive(PositiveImbalance::new(value - account.free))
		} else {
			SignedImbalance::Negative(NegativeImbalance::new(account.free - value))
		};
		account.free = value;

		// If the balance is too low, then the account is reaped.
		// Free balance can never be less than ED. If that happens, it gets reduced to zero
		// and the account information relevant to this subsystem is deleted (i.e. the
		// account is reaped).
		let outcome = Self::set_account(who, &account, &old_account);
		(imbalance, outcome)
	}
}

impl<T: Trait<I>, I: Instance> ReservableCurrency<T::AccountId> for Module<T, I>  where
	T::Balance: MaybeSerializeDeserialize + Debug
{
	/// Check if `who` can reserve `value` from their free balance.
	///
	/// Always `true` if value to be reserved is zero.
	fn can_reserve(who: &T::AccountId, value: Self::Balance) -> bool {
		if value.is_zero() { return true }
		Self::account(who).free
			.checked_sub(&value)
			.map_or(false, |new_balance|
				Self::ensure_can_withdraw(who, value, WithdrawReason::Reserve.into(), new_balance).is_ok()
			)
	}

	fn reserved_balance(who: &T::AccountId) -> Self::Balance {
		Self::account(who).reserved
	}

	/// Move `value` from the free balance from `who` to their reserved balance.
	///
	/// Is a no-op if value to be reserved is zero.
	fn reserve(who: &T::AccountId, value: Self::Balance) -> result::Result<(), DispatchError> {
		if value.is_zero() { return Ok(()) }

		let old_account = Self::account(who);
		let mut account = old_account.clone();

		account.free = account.free.checked_sub(&value).ok_or(Error::<T, I>::InsufficientBalance)?;
		account.reserved = account.reserved.checked_add(&value).ok_or(Error::<T, I>::Overflow)?;
		Self::ensure_can_withdraw(who, value, WithdrawReason::Reserve.into(), account.free)?;

		Self::set_account(who, &account, &old_account);
		Ok(())
	}

	/// Unreserve some funds, returning any amount that was unable to be unreserved.
	///
	/// Is a no-op if the value to be unreserved is zero.
	fn unreserve(who: &T::AccountId, value: Self::Balance) -> Self::Balance {
		if value.is_zero() { return Zero::zero() }

		let old_account = Self::account(who);
		let mut account = old_account.clone();

		let actual = cmp::min(account.reserved, value);
		account.reserved -= actual;
		// defensive only: this can never fail since total issuance which is at least free+reserved
		// fits into the same datatype.
		account.free = account.free.saturating_add(actual);

		Self::set_account(who, &account, &old_account);

		value - actual
	}

	/// Slash from reserved balance, returning the negative imbalance created,
	/// and any amount that was unable to be slashed.
	///
	/// Is a no-op if the value to be slashed is zero.
	fn slash_reserved(
		who: &T::AccountId,
		value: Self::Balance
	) -> (Self::NegativeImbalance, Self::Balance) {
		if value.is_zero() { return (NegativeImbalance::zero(), Zero::zero()) }

		let old_account = Self::account(who);
		let mut account = old_account.clone();

		// underflow should never happen, but it if does, there's nothing to be done here.
		let actual = cmp::min(account.reserved, value);
		account.reserved -= actual;

		Self::set_account(who, &account, &old_account);

		(NegativeImbalance::new(actual), value - actual)
	}

	/// Move the reserved balance of one account into the free balance of another.
	///
	/// Is a no-op if the value to be moved is zero.
	fn repatriate_reserved(
		slashed: &T::AccountId,
		beneficiary: &T::AccountId,
		value: Self::Balance,
	) -> result::Result<Self::Balance, DispatchError> {
		if value.is_zero() { return Ok (Zero::zero()) }

		if slashed == beneficiary {
			return Ok(Self::unreserve(slashed, value));
		}

		let old_to_account = Self::account(beneficiary);
		let mut to_account = old_to_account.clone();
		ensure!(!to_account.total().is_zero(), Error::<T, I>::DeadAccount);

		let old_from_account = Self::account(slashed);
		let mut from_account = old_from_account.clone();
		let actual = cmp::min(from_account.reserved, value);

		to_account.free = to_account.free.checked_add(&actual).ok_or(Error::<T, I>::Overflow)?;
		from_account.reserved -= actual;

		Self::set_account(slashed, &from_account, &old_from_account);
		Self::set_account(beneficiary, &to_account, &old_to_account);

		Ok(value - actual)
	}
}

impl<T: Trait<I>, I: Instance> LockableCurrency<T::AccountId> for Module<T, I>
where
	T::Balance: MaybeSerializeDeserialize + Debug
{
	type Moment = T::BlockNumber;

	// Set a lock on the balance of `who`.
	// Is a no-op if lock amount is zero or `reasons` `is_none()`.
	fn set_lock(
		id: LockIdentifier,
		who: &T::AccountId,
		amount: T::Balance,
		reasons: WithdrawReasons,
	) {
		if amount.is_zero() || reasons.is_none() { return }
		let mut new_lock = Some(BalanceLock { id, amount, reasons: reasons.into() });
		let mut locks = Self::locks(who).into_iter().filter_map(|l|
			if l.id == id {
				new_lock.take()
			} else {
				Some(l)
			}).collect::<Vec<_>>();
		if let Some(lock) = new_lock {
			locks.push(lock)
		}
		Self::update_locks(who, &locks[..]);
	}

	// Extend a lock on the balance of `who`.
	// Is a no-op if lock amount is zero or `reasons` `is_none()`.
	fn extend_lock(
		id: LockIdentifier,
		who: &T::AccountId,
		amount: T::Balance,
		reasons: WithdrawReasons,
	) {
		if amount.is_zero() || reasons.is_none() { return }
		let mut new_lock = Some(BalanceLock { id, amount, reasons: reasons.into() });
		let mut locks = Self::locks(who).into_iter().filter_map(|l|
			if l.id == id {
				new_lock.take().map(|nl| {
					BalanceLock {
						id: l.id,
						amount: l.amount.max(nl.amount),
						reasons: l.reasons | nl.reasons,
					}
				})
			} else {
				Some(l)
			}).collect::<Vec<_>>();
		if let Some(lock) = new_lock {
			locks.push(lock)
		}
		Self::update_locks(who, &locks[..]);
	}

	fn remove_lock(
		id: LockIdentifier,
		who: &T::AccountId,
	) {
		let mut locks = Self::locks(who);
		locks.retain(|l| l.id != id);
		Self::update_locks(who, &locks[..]);
	}
}

impl<T: Trait<I>, I: Instance> IsDeadAccount<T::AccountId> for Module<T, I>
where
	T::Balance: MaybeSerializeDeserialize + Debug
{
	fn is_dead_account(who: &T::AccountId) -> bool {
		// this should always be exactly equivalent to `Self::account(who).total().is_zero()`
		!Account::<T, I>::contains_key(who)
	}
}