git.delta.rocks / unique-network / refs/commits / d2b5cc3bc7de

1// Copyright 2019-2022 Unique Network (Gibraltar) Ltd.2// This file is part of Unique Network.34// Unique Network is free software: you can redistribute it and/or modify5// it under the terms of the GNU General Public License as published by6// the Free Software Foundation, either version 3 of the License, or7// (at your option) any later version.89// Unique Network is distributed in the hope that it will be useful,10// but WITHOUT ANY WARRANTY; without even the implied warranty of11// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the12// GNU General Public License for more details.1314// You should have received a copy of the GNU General Public License15// along with Unique Network. If not, see <http://www.gnu.org/licenses/>.1617//! # Fungible Pallet18//!19//! The Fungible pallet provides functionality for dealing with fungible assets.20//!21//! - [`CreateItemData`]22//! - [`Config`]23//! - [`FungibleHandle`]24//! - [`Pallet`]25//! - [`TotalSupply`]26//! - [`Balance`]27//! - [`Allowance`]28//! - [`Error`]29//!30//! ## Fungible tokens31//!32//! Fungible tokens or assets are divisible and non-unique. For instance,33//! fiat currencies like the dollar are fungible: A $1 bill34//! in New York City has the same value as a $1 bill in Miami.35//! A fungible token can also be a cryptocurrency like Bitcoin: 1 BTC is worth 1 BTC,36//! no matter where it is issued. Thus, the fungibility refers to a specific currency’s37//! ability to maintain one standard value. As well, it needs to have uniform acceptance.38//! This means that a currency’s history should not be able to affect its value,39//! and this is due to the fact that each piece that is a part of the currency is equal40//! in value when compared to every other piece of that exact same currency.41//! In the world of cryptocurrencies, this is essentially a coin or a token42//! that can be replaced by another identical coin or token, and they are43//! both mutually interchangeable. A popular implementation of fungible tokens is44//! the ERC-20 token standard.45//!46//! ### ERC-2047//!48//! The [ERC-20](https://ethereum.org/en/developers/docs/standards/tokens/erc-20/) (Ethereum Request for Comments 20), proposed by Fabian Vogelsteller in November 2015,49//! is a Token Standard that implements an API for tokens within Smart Contracts.50//!51//! Example functionalities ERC-20 provides:52//!53//! * transfer tokens from one account to another54//! * get the current token balance of an account55//! * get the total supply of the token available on the network56//! * approve whether an amount of token from an account can be spent by a third-party account57//!58//! ## Overview59//!60//! The module provides functionality for asset management of fungible asset, supports ERC-20 standart, includes:61//!62//! * Asset Issuance63//! * Asset Transferal64//! * Asset Destruction65//! * Delegated Asset Transfers66//!67//! **NOTE:** The created fungible asset always has `token_id` = 0.68//! So `tokenA` and `tokenB` will have different `collection_id`.69//!70//! ### Implementations71//!72//! The Fungible pallet provides implementations for the following traits.73//!74//! - [`WithRecorder`](pallet_evm_coder_substrate::WithRecorder): Trait for EVM support75//! - [`CommonCollectionOperations`](pallet_common::CommonCollectionOperations): Functions for dealing with collections76//!	- [`CommonWeightInfo`](pallet_common::CommonWeightInfo): Functions for retrieval of transaction weight77//! - [`CommonEvmHandler`](pallet_common::erc::CommonEvmHandler): Function for handling EVM runtime calls7879#![cfg_attr(not(feature = "std"), no_std)]8081use core::ops::Deref;82use evm_coder::ToLog;83use frame_support::{ensure};84use pallet_evm::account::CrossAccountId;85use up_data_structs::{86	AccessMode, CollectionId, TokenId, CreateCollectionData, mapping::TokenAddressMapping,87	budget::Budget,88};89use pallet_common::{90	Error as CommonError, Event as CommonEvent, Pallet as PalletCommon,91	eth::collection_id_to_address,92};93use pallet_evm::Pallet as PalletEvm;94use pallet_structure::Pallet as PalletStructure;95use pallet_evm_coder_substrate::WithRecorder;96use sp_core::H160;97use sp_runtime::{ArithmeticError, DispatchError, DispatchResult};98use sp_std::{collections::btree_map::BTreeMap, vec::Vec};99100pub use pallet::*;101102use crate::erc::ERC20Events;103#[cfg(feature = "runtime-benchmarks")]104pub mod benchmarking;105pub mod common;106pub mod erc;107pub mod weights;108109pub type CreateItemData<T> = (<T as pallet_evm::account::Config>::CrossAccountId, u128);110pub(crate) type SelfWeightOf<T> = <T as Config>::WeightInfo;111112#[frame_support::pallet]113pub mod pallet {114	use frame_support::{Blake2_128, Blake2_128Concat, Twox64Concat, pallet_prelude::*, storage::Key};115	use up_data_structs::CollectionId;116	use super::weights::WeightInfo;117118	#[pallet::error]119	pub enum Error<T> {120		/// Not Fungible item data used to mint in Fungible collection.121		NotFungibleDataUsedToMintFungibleCollectionToken,122		/// Fungible tokens hold no ID, and the default value of TokenId for Fungible collection is 0.123		FungibleItemsHaveNoId,124		/// Tried to set data for fungible item.125		FungibleItemsDontHaveData,126		/// Fungible token does not support nesting.127		FungibleDisallowsNesting,128		/// Setting item properties is not allowed.129		SettingPropertiesNotAllowed,130	}131132	#[pallet::config]133	pub trait Config:134		frame_system::Config + pallet_common::Config + pallet_structure::Config + pallet_evm::Config135	{136		type WeightInfo: WeightInfo;137	}138139	#[pallet::pallet]140	#[pallet::generate_store(pub(super) trait Store)]141	pub struct Pallet<T>(_);142143	/// Total amount of fungible tokens inside a collection.144	#[pallet::storage]145	pub type TotalSupply<T: Config> =146		StorageMap<Hasher = Twox64Concat, Key = CollectionId, Value = u128, QueryKind = ValueQuery>;147148	/// Amount of tokens owned by an account inside a collection.149	#[pallet::storage]150	pub type Balance<T: Config> = StorageNMap<151		Key = (152			Key<Twox64Concat, CollectionId>,153			Key<Blake2_128Concat, T::CrossAccountId>,154		),155		Value = u128,156		QueryKind = ValueQuery,157	>;158159	/// Storage for assets delegated to a limited extent to other users.160	#[pallet::storage]161	pub type Allowance<T: Config> = StorageNMap<162		Key = (163			Key<Twox64Concat, CollectionId>,164			Key<Blake2_128, T::CrossAccountId>,165			Key<Blake2_128Concat, T::CrossAccountId>,166		),167		Value = u128,168		QueryKind = ValueQuery,169	>;170171	/// Foreign collection flag172	#[pallet::storage]173	pub type ForeignCollection<T: Config> =174		StorageMap<Hasher = Twox64Concat, Key = CollectionId, Value = bool, QueryKind = ValueQuery>;175}176177/// Wrapper around untyped collection handle, asserting inner collection is of fungible type.178/// Required for interaction with Fungible collections, type safety and implementation [`solidity_interface`][`evm_coder::solidity_interface`].179pub struct FungibleHandle<T: Config>(pallet_common::CollectionHandle<T>);180181/// Implementation of methods required for dispatching during runtime.182impl<T: Config> FungibleHandle<T> {183	/// Casts [`CollectionHandle`][`pallet_common::CollectionHandle`] into [`FungibleHandle`].184	pub fn cast(inner: pallet_common::CollectionHandle<T>) -> Self {185		Self(inner)186	}187188	/// Casts [`FungibleHandle`] into [`CollectionHandle`][`pallet_common::CollectionHandle`].189	pub fn into_inner(self) -> pallet_common::CollectionHandle<T> {190		self.0191	}192	/// Returns a mutable reference to the internal [`CollectionHandle`][`pallet_common::CollectionHandle`].193	pub fn common_mut(&mut self) -> &mut pallet_common::CollectionHandle<T> {194		&mut self.0195	}196}197impl<T: Config> WithRecorder<T> for FungibleHandle<T> {198	fn recorder(&self) -> &pallet_evm_coder_substrate::SubstrateRecorder<T> {199		self.0.recorder()200	}201	fn into_recorder(self) -> pallet_evm_coder_substrate::SubstrateRecorder<T> {202		self.0.into_recorder()203	}204}205impl<T: Config> Deref for FungibleHandle<T> {206	type Target = pallet_common::CollectionHandle<T>;207208	fn deref(&self) -> &Self::Target {209		&self.0210	}211}212213/// Pallet implementation for fungible assets214impl<T: Config> Pallet<T> {215	/// Initializes the collection. Returns [CollectionId] on success, [DispatchError] otherwise.216	pub fn init_collection(217		owner: T::CrossAccountId,218		data: CreateCollectionData<T::AccountId>,219	) -> Result<CollectionId, DispatchError> {220		<PalletCommon<T>>::init_collection(owner, data, false)221	}222223	/// Initializes the collection with ForeignCollection flag. Returns [CollectionId] on success, [DispatchError] otherwise.224	pub fn init_foreign_collection(225		owner: T::CrossAccountId,226		data: CreateCollectionData<T::AccountId>,227	) -> Result<CollectionId, DispatchError> {228		let id = <PalletCommon<T>>::init_collection(owner, data, false)?;229		<ForeignCollection<T>>::insert(id, true);230		Ok(id)231	}232233	/// Destroys a collection.234	pub fn destroy_collection(235		collection: FungibleHandle<T>,236		sender: &T::CrossAccountId,237	) -> DispatchResult {238		let id = collection.id;239240		if Self::collection_has_tokens(id) {241			return Err(<CommonError<T>>::CantDestroyNotEmptyCollection.into());242		}243244		// =========245246		PalletCommon::destroy_collection(collection.0, sender)?;247248		<ForeignCollection<T>>::remove(id);249		<TotalSupply<T>>::remove(id);250		let _ = <Balance<T>>::clear_prefix((id,), u32::MAX, None);251		let _ = <Allowance<T>>::clear_prefix((id,), u32::MAX, None);252		Ok(())253	}254255	///Checks if collection has tokens. Return `true` if it has.256	fn collection_has_tokens(collection_id: CollectionId) -> bool {257		<TotalSupply<T>>::get(collection_id) != 0258	}259260	/// Burns the specified amount of the token. If the token balance261	/// or total supply is less than the given value,262	/// it will return [DispatchError].263	pub fn burn(264		collection: &FungibleHandle<T>,265		owner: &T::CrossAccountId,266		amount: u128,267	) -> DispatchResult {268		let total_supply = <TotalSupply<T>>::get(collection.id)269			.checked_sub(amount)270			.ok_or(<CommonError<T>>::TokenValueTooLow)?;271272		let balance = <Balance<T>>::get((collection.id, owner))273			.checked_sub(amount)274			.ok_or(<CommonError<T>>::TokenValueTooLow)?;275276		// Foreign collection check277		ensure!(278			!<ForeignCollection<T>>::get(collection.id),279			<CommonError<T>>::NoPermission280		);281282		if collection.permissions.access() == AccessMode::AllowList {283			collection.check_allowlist(owner)?;284		}285286		// =========287288		if balance == 0 {289			<Balance<T>>::remove((collection.id, owner));290			<PalletStructure<T>>::unnest_if_nested(owner, collection.id, TokenId::default());291		} else {292			<Balance<T>>::insert((collection.id, owner), balance);293		}294		<TotalSupply<T>>::insert(collection.id, total_supply);295296		<PalletEvm<T>>::deposit_log(297			ERC20Events::Transfer {298				from: *owner.as_eth(),299				to: H160::default(),300				value: amount.into(),301			}302			.to_log(collection_id_to_address(collection.id)),303		);304		<PalletCommon<T>>::deposit_event(CommonEvent::ItemDestroyed(305			collection.id,306			TokenId::default(),307			owner.clone(),308			amount,309		));310		Ok(())311	}312313	/// Burns the specified amount of the token.314	pub fn burn_foreign(315		collection: &FungibleHandle<T>,316		owner: &T::CrossAccountId,317		amount: u128,318	) -> DispatchResult {319		let total_supply = <TotalSupply<T>>::get(collection.id)320			.checked_sub(amount)321			.ok_or(<CommonError<T>>::TokenValueTooLow)?;322323		let balance = <Balance<T>>::get((collection.id, owner))324			.checked_sub(amount)325			.ok_or(<CommonError<T>>::TokenValueTooLow)?;326		// =========327328		if balance == 0 {329			<Balance<T>>::remove((collection.id, owner));330			<PalletStructure<T>>::unnest_if_nested(owner, collection.id, TokenId::default());331		} else {332			<Balance<T>>::insert((collection.id, owner), balance);333		}334		<TotalSupply<T>>::insert(collection.id, total_supply);335336		<PalletEvm<T>>::deposit_log(337			ERC20Events::Transfer {338				from: *owner.as_eth(),339				to: H160::default(),340				value: amount.into(),341			}342			.to_log(collection_id_to_address(collection.id)),343		);344		<PalletCommon<T>>::deposit_event(CommonEvent::ItemDestroyed(345			collection.id,346			TokenId::default(),347			owner.clone(),348			amount,349		));350		Ok(())351	}352353	/// Transfers the specified amount of tokens. Will check that354	/// the transfer is allowed for the token.355	///356	/// - `from`: Owner of tokens to transfer.357	/// - `to`: Recepient of transfered tokens.358	/// - `amount`: Amount of tokens to transfer.359	/// - `collection`: Collection that contains the token360	pub fn transfer(361		collection: &FungibleHandle<T>,362		from: &T::CrossAccountId,363		to: &T::CrossAccountId,364		amount: u128,365		nesting_budget: &dyn Budget,366	) -> DispatchResult {367		ensure!(368			collection.limits.transfers_enabled(),369			<CommonError<T>>::TransferNotAllowed,370		);371372		if collection.permissions.access() == AccessMode::AllowList {373			collection.check_allowlist(from)?;374			collection.check_allowlist(to)?;375		}376		<PalletCommon<T>>::ensure_correct_receiver(to)?;377378		let balance_from = <Balance<T>>::get((collection.id, from))379			.checked_sub(amount)380			.ok_or(<CommonError<T>>::TokenValueTooLow)?;381		let balance_to = if from != to {382			Some(383				<Balance<T>>::get((collection.id, to))384					.checked_add(amount)385					.ok_or(ArithmeticError::Overflow)?,386			)387		} else {388			None389		};390391		// =========392393		<PalletStructure<T>>::nest_if_sent_to_token(394			from.clone(),395			to,396			collection.id,397			TokenId::default(),398			nesting_budget,399		)?;400401		if let Some(balance_to) = balance_to {402			// from != to403			if balance_from == 0 {404				<Balance<T>>::remove((collection.id, from));405				<PalletStructure<T>>::unnest_if_nested(from, collection.id, TokenId::default());406			} else {407				<Balance<T>>::insert((collection.id, from), balance_from);408			}409			<Balance<T>>::insert((collection.id, to), balance_to);410		}411412		<PalletEvm<T>>::deposit_log(413			ERC20Events::Transfer {414				from: *from.as_eth(),415				to: *to.as_eth(),416				value: amount.into(),417			}418			.to_log(collection_id_to_address(collection.id)),419		);420		<PalletCommon<T>>::deposit_event(CommonEvent::Transfer(421			collection.id,422			TokenId::default(),423			from.clone(),424			to.clone(),425			amount,426		));427		Ok(())428	}429430	/// Minting tokens for multiple IDs.431	/// See [`create_item`][`Pallet::create_item`] for more details.432	pub fn create_multiple_items(433		collection: &FungibleHandle<T>,434		sender: &T::CrossAccountId,435		data: BTreeMap<T::CrossAccountId, u128>,436		nesting_budget: &dyn Budget,437	) -> DispatchResult {438		// Foreign collection check439		ensure!(440			!<ForeignCollection<T>>::get(collection.id),441			<CommonError<T>>::NoPermission442		);443444		if !collection.is_owner_or_admin(sender) {445			ensure!(446				collection.permissions.mint_mode(),447				<CommonError<T>>::PublicMintingNotAllowed448			);449			collection.check_allowlist(sender)?;450451			for (owner, _) in data.iter() {452				collection.check_allowlist(owner)?;453			}454		}455456		let total_supply = data457			.iter()458			.map(|(_, v)| *v)459			.try_fold(<TotalSupply<T>>::get(collection.id), |acc, v| {460				acc.checked_add(v)461			})462			.ok_or(ArithmeticError::Overflow)?;463464		for (to, _) in data.iter() {465			<PalletStructure<T>>::check_nesting(466				sender.clone(),467				to,468				collection.id,469				TokenId::default(),470				nesting_budget,471			)?;472		}473474		let updated_balances = data475			.into_iter()476			.map(|(user, amount)| {477				let updated_balance = <Balance<T>>::get((collection.id, &user))478					.checked_add(amount)479					.ok_or(ArithmeticError::Overflow)?;480				Ok((user, amount, updated_balance))481			})482			.collect::<Result<Vec<_>, DispatchError>>()?;483484		// =========485486		<TotalSupply<T>>::insert(collection.id, total_supply);487		for (user, amount, updated_balance) in updated_balances {488			<Balance<T>>::insert((collection.id, &user), updated_balance);489			<PalletStructure<T>>::nest_if_sent_to_token_unchecked(490				&user,491				collection.id,492				TokenId::default(),493			);494			<PalletEvm<T>>::deposit_log(495				ERC20Events::Transfer {496					from: H160::default(),497					to: *user.as_eth(),498					value: amount.into(),499				}500				.to_log(collection_id_to_address(collection.id)),501			);502			<PalletCommon<T>>::deposit_event(CommonEvent::ItemCreated(503				collection.id,504				TokenId::default(),505				user.clone(),506				amount,507			));508		}509510		Ok(())511	}512513	/// Minting tokens for multiple IDs.514	/// See [`create_item_foreign`][`Pallet::create_item_foreign`] for more details.515	pub fn create_multiple_items_foreign(516		collection: &FungibleHandle<T>,517		sender: &T::CrossAccountId,518		data: BTreeMap<T::CrossAccountId, u128>,519		nesting_budget: &dyn Budget,520	) -> DispatchResult {521		let total_supply = data522			.iter()523			.map(|(_, v)| *v)524			.try_fold(<TotalSupply<T>>::get(collection.id), |acc, v| {525				acc.checked_add(v)526			})527			.ok_or(ArithmeticError::Overflow)?;528529		let mut balances = data;530		for (k, v) in balances.iter_mut() {531			*v = <Balance<T>>::get((collection.id, &k))532				.checked_add(*v)533				.ok_or(ArithmeticError::Overflow)?;534		}535536		for (to, _) in balances.iter() {537			<PalletStructure<T>>::check_nesting(538				sender.clone(),539				to,540				collection.id,541				TokenId::default(),542				nesting_budget,543			)?;544		}545546		// =========547548		<TotalSupply<T>>::insert(collection.id, total_supply);549		for (user, amount) in balances {550			<Balance<T>>::insert((collection.id, &user), amount);551			<PalletStructure<T>>::nest_if_sent_to_token_unchecked(552				&user,553				collection.id,554				TokenId::default(),555			);556			<PalletEvm<T>>::deposit_log(557				ERC20Events::Transfer {558					from: H160::default(),559					to: *user.as_eth(),560					value: amount.into(),561				}562				.to_log(collection_id_to_address(collection.id)),563			);564			<PalletCommon<T>>::deposit_event(CommonEvent::ItemCreated(565				collection.id,566				TokenId::default(),567				user.clone(),568				amount,569			));570		}571572		Ok(())573	}574575	fn set_allowance_unchecked(576		collection: &FungibleHandle<T>,577		owner: &T::CrossAccountId,578		spender: &T::CrossAccountId,579		amount: u128,580	) {581		if amount == 0 {582			<Allowance<T>>::remove((collection.id, owner, spender));583		} else {584			<Allowance<T>>::insert((collection.id, owner, spender), amount);585		}586587		<PalletEvm<T>>::deposit_log(588			ERC20Events::Approval {589				owner: *owner.as_eth(),590				spender: *spender.as_eth(),591				value: amount.into(),592			}593			.to_log(collection_id_to_address(collection.id)),594		);595		<PalletCommon<T>>::deposit_event(CommonEvent::Approved(596			collection.id,597			TokenId(0),598			owner.clone(),599			spender.clone(),600			amount,601		));602	}603604	/// Set allowance for the spender to `transfer` or `burn` owner's tokens.605	///606	/// - `collection`: Collection that contains the token607	/// - `owner`: Owner of tokens that sets the allowance.608	/// - `spender`: Recipient of the allowance rights.609	/// - `amount`: Amount of tokens the spender is allowed to `transfer` or `burn`.610	pub fn set_allowance(611		collection: &FungibleHandle<T>,612		owner: &T::CrossAccountId,613		spender: &T::CrossAccountId,614		amount: u128,615	) -> DispatchResult {616		if collection.permissions.access() == AccessMode::AllowList {617			collection.check_allowlist(owner)?;618			collection.check_allowlist(spender)?;619		}620621		if <Balance<T>>::get((collection.id, owner)) < amount {622			ensure!(623				collection.ignores_owned_amount(owner),624				<CommonError<T>>::CantApproveMoreThanOwned625			);626		}627628		// =========629630		Self::set_allowance_unchecked(collection, owner, spender, amount);631		Ok(())632	}633634	/// Checks if a non-owner has (enough) allowance from the owner to perform operations on the tokens.635	/// Returns the expected remaining allowance - it should be set manually if the transaction proceeds.636	///637	/// - `collection`: Collection that contains the token.638	/// - `spender`: CrossAccountId who has the allowance rights.639	/// - `from`: The owner of the tokens who sets the allowance.640	/// - `amount`: Amount of tokens by which the allowance sholud be reduced.641	fn check_allowed(642		collection: &FungibleHandle<T>,643		spender: &T::CrossAccountId,644		from: &T::CrossAccountId,645		amount: u128,646		nesting_budget: &dyn Budget,647	) -> Result<Option<u128>, DispatchError> {648		if spender.conv_eq(from) {649			return Ok(None);650		}651		if collection.permissions.access() == AccessMode::AllowList {652			// `from`, `to` checked in [`transfer`]653			collection.check_allowlist(spender)?;654		}655		if let Some(source) = T::CrossTokenAddressMapping::address_to_token(from) {656			// TODO: should collection owner be allowed to perform this transfer?657			ensure!(658				<PalletStructure<T>>::check_indirectly_owned(659					spender.clone(),660					source.0,661					source.1,662					None,663					nesting_budget664				)?,665				<CommonError<T>>::ApprovedValueTooLow,666			);667			return Ok(None);668		}669		let allowance = <Allowance<T>>::get((collection.id, from, spender)).checked_sub(amount);670		if allowance.is_none() {671			ensure!(672				collection.ignores_allowance(spender),673				<CommonError<T>>::ApprovedValueTooLow674			);675		}676677		Ok(allowance)678	}679680	/// Transfer fungible tokens from one account to another.681	/// Same as the [`transfer`][`Pallet::transfer`] but spender doesn't needs to be an owner of the token pieces.682	/// The owner should set allowance for the spender to transfer pieces.683	///	See [`set_allowance`][`Pallet::set_allowance`] for more details.684685	pub fn transfer_from(686		collection: &FungibleHandle<T>,687		spender: &T::CrossAccountId,688		from: &T::CrossAccountId,689		to: &T::CrossAccountId,690		amount: u128,691		nesting_budget: &dyn Budget,692	) -> DispatchResult {693		let allowance = Self::check_allowed(collection, spender, from, amount, nesting_budget)?;694695		// =========696697		Self::transfer(collection, from, to, amount, nesting_budget)?;698		if let Some(allowance) = allowance {699			Self::set_allowance_unchecked(collection, from, spender, allowance);700		}701		Ok(())702	}703704	/// Burn fungible tokens from the account.705	///706	/// Same as the [`burn`][`Pallet::burn`] but spender doesn't need to be an owner of the tokens. The `from` should707	/// set allowance for the spender to burn tokens.708	/// See [`set_allowance`][`Pallet::set_allowance`] for more details.709	pub fn burn_from(710		collection: &FungibleHandle<T>,711		spender: &T::CrossAccountId,712		from: &T::CrossAccountId,713		amount: u128,714		nesting_budget: &dyn Budget,715	) -> DispatchResult {716		let allowance = Self::check_allowed(collection, spender, from, amount, nesting_budget)?;717718		// =========719720		Self::burn(collection, from, amount)?;721		if let Some(allowance) = allowance {722			Self::set_allowance_unchecked(collection, from, spender, allowance);723		}724		Ok(())725	}726727	///	Creates fungible token.728	///729	/// The sender should be the owner/admin of the collection or collection should be configured730	/// to allow public minting.731	///732	/// - `data`: Contains user who will become the owners of the tokens and amount733	///   of tokens he will receive.734	pub fn create_item(735		collection: &FungibleHandle<T>,736		sender: &T::CrossAccountId,737		data: CreateItemData<T>,738		nesting_budget: &dyn Budget,739	) -> DispatchResult {740		Self::create_multiple_items(741			collection,742			sender,743			[(data.0, data.1)].into_iter().collect(),744			nesting_budget,745		)746	}747748	///	Creates fungible token.749	///750	/// - `data`: Contains user who will become the owners of the tokens and amount751	///   of tokens he will receive.752	pub fn create_item_foreign(753		collection: &FungibleHandle<T>,754		sender: &T::CrossAccountId,755		data: CreateItemData<T>,756		nesting_budget: &dyn Budget,757	) -> DispatchResult {758		Self::create_multiple_items_foreign(759			collection,760			sender,761			[(data.0, data.1)].into_iter().collect(),762			nesting_budget,763		)764	}765766	/// Returns 10 tokens owners in no particular order767	///768	/// There is no direct way to get token holders in ascending order,769	/// since `iter_prefix` returns values in no particular order.770	/// Therefore, getting the 10 largest holders with a large value of holders771	/// can lead to impact memory allocation + sorting with  `n * log (n)`.772	pub fn token_owners(773		collection: CollectionId,774		_token: TokenId,775	) -> Option<Vec<T::CrossAccountId>> {776		let res: Vec<T::CrossAccountId> = <Balance<T>>::iter_prefix((collection,))777			.map(|(owner, _amount)| owner)778			.take(10)779			.collect();780781		if res.is_empty() {782			None783		} else {784			Some(res)785		}786	}787}