git.delta.rocks / unique-network / refs/commits / 0c40eab5740e

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, CollectionFlags, TokenId, CreateCollectionData,87	mapping::TokenAddressMapping, 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::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	>;170}171172/// Wrapper around untyped collection handle, asserting inner collection is of fungible type.173/// Required for interaction with Fungible collections, type safety and implementation [`solidity_interface`][`evm_coder::solidity_interface`].174pub struct FungibleHandle<T: Config>(pallet_common::CollectionHandle<T>);175176/// Implementation of methods required for dispatching during runtime.177impl<T: Config> FungibleHandle<T> {178	/// Casts [`CollectionHandle`][`pallet_common::CollectionHandle`] into [`FungibleHandle`].179	pub fn cast(inner: pallet_common::CollectionHandle<T>) -> Self {180		Self(inner)181	}182183	/// Casts [`FungibleHandle`] into [`CollectionHandle`][`pallet_common::CollectionHandle`].184	pub fn into_inner(self) -> pallet_common::CollectionHandle<T> {185		self.0186	}187	/// Returns a mutable reference to the internal [`CollectionHandle`][`pallet_common::CollectionHandle`].188	pub fn common_mut(&mut self) -> &mut pallet_common::CollectionHandle<T> {189		&mut self.0190	}191}192impl<T: Config> WithRecorder<T> for FungibleHandle<T> {193	fn recorder(&self) -> &pallet_evm_coder_substrate::SubstrateRecorder<T> {194		self.0.recorder()195	}196	fn into_recorder(self) -> pallet_evm_coder_substrate::SubstrateRecorder<T> {197		self.0.into_recorder()198	}199}200impl<T: Config> Deref for FungibleHandle<T> {201	type Target = pallet_common::CollectionHandle<T>;202203	fn deref(&self) -> &Self::Target {204		&self.0205	}206}207208/// Pallet implementation for fungible assets209impl<T: Config> Pallet<T> {210	/// Initializes the collection. Returns [CollectionId] on success, [DispatchError] otherwise.211	pub fn init_collection(212		owner: T::CrossAccountId,213		payer: T::CrossAccountId,214		data: CreateCollectionData<T::AccountId>,215		flags: CollectionFlags,216	) -> Result<CollectionId, DispatchError> {217		<PalletCommon<T>>::init_collection(owner, payer, data, flags)218	}219220	/// Initializes the collection with ForeignCollection flag. Returns [CollectionId] on success, [DispatchError] otherwise.221	pub fn init_foreign_collection(222		owner: T::CrossAccountId,223		payer: T::CrossAccountId,224		data: CreateCollectionData<T::AccountId>,225	) -> Result<CollectionId, DispatchError> {226		let id = <PalletCommon<T>>::init_collection(227			owner,228			payer,229			data,230			CollectionFlags {231				foreign: true,232				..Default::default()233			},234		)?;235		Ok(id)236	}237238	/// Destroys a collection.239	pub fn destroy_collection(240		collection: FungibleHandle<T>,241		sender: &T::CrossAccountId,242	) -> DispatchResult {243		let id = collection.id;244245		if Self::collection_has_tokens(id) {246			return Err(<CommonError<T>>::CantDestroyNotEmptyCollection.into());247		}248249		// =========250251		PalletCommon::destroy_collection(collection.0, sender)?;252253		<TotalSupply<T>>::remove(id);254		let _ = <Balance<T>>::clear_prefix((id,), u32::MAX, None);255		let _ = <Allowance<T>>::clear_prefix((id,), u32::MAX, None);256		Ok(())257	}258259	///Checks if collection has tokens. Return `true` if it has.260	fn collection_has_tokens(collection_id: CollectionId) -> bool {261		<TotalSupply<T>>::get(collection_id) != 0262	}263264	/// Burns the specified amount of the token. If the token balance265	/// or total supply is less than the given value,266	/// it will return [DispatchError].267	pub fn burn(268		collection: &FungibleHandle<T>,269		owner: &T::CrossAccountId,270		amount: u128,271	) -> DispatchResult {272		let total_supply = <TotalSupply<T>>::get(collection.id)273			.checked_sub(amount)274			.ok_or(<CommonError<T>>::TokenValueTooLow)?;275276		let balance = <Balance<T>>::get((collection.id, owner))277			.checked_sub(amount)278			.ok_or(<CommonError<T>>::TokenValueTooLow)?;279280		// Foreign collection check281		ensure!(!collection.flags.foreign, <CommonError<T>>::NoPermission);282283		if collection.permissions.access() == AccessMode::AllowList {284			collection.check_allowlist(owner)?;285		}286287		// =========288289		if balance == 0 {290			<Balance<T>>::remove((collection.id, owner));291			<PalletStructure<T>>::unnest_if_nested(owner, collection.id, TokenId::default());292		} else {293			<Balance<T>>::insert((collection.id, owner), balance);294		}295		<TotalSupply<T>>::insert(collection.id, total_supply);296297		<PalletEvm<T>>::deposit_log(298			ERC20Events::Transfer {299				from: *owner.as_eth(),300				to: H160::default(),301				value: amount.into(),302			}303			.to_log(collection_id_to_address(collection.id)),304		);305		<PalletCommon<T>>::deposit_event(CommonEvent::ItemDestroyed(306			collection.id,307			TokenId::default(),308			owner.clone(),309			amount,310		));311		Ok(())312	}313314	/// Burns the specified amount of the token.315	pub fn burn_foreign(316		collection: &FungibleHandle<T>,317		owner: &T::CrossAccountId,318		amount: u128,319	) -> DispatchResult {320		let total_supply = <TotalSupply<T>>::get(collection.id)321			.checked_sub(amount)322			.ok_or(<CommonError<T>>::TokenValueTooLow)?;323324		let balance = <Balance<T>>::get((collection.id, owner))325			.checked_sub(amount)326			.ok_or(<CommonError<T>>::TokenValueTooLow)?;327		// =========328329		if balance == 0 {330			<Balance<T>>::remove((collection.id, owner));331			<PalletStructure<T>>::unnest_if_nested(owner, collection.id, TokenId::default());332		} else {333			<Balance<T>>::insert((collection.id, owner), balance);334		}335		<TotalSupply<T>>::insert(collection.id, total_supply);336337		<PalletEvm<T>>::deposit_log(338			ERC20Events::Transfer {339				from: *owner.as_eth(),340				to: H160::default(),341				value: amount.into(),342			}343			.to_log(collection_id_to_address(collection.id)),344		);345		<PalletCommon<T>>::deposit_event(CommonEvent::ItemDestroyed(346			collection.id,347			TokenId::default(),348			owner.clone(),349			amount,350		));351		Ok(())352	}353354	/// Transfers the specified amount of tokens. Will check that355	/// the transfer is allowed for the token.356	///357	/// - `from`: Owner of tokens to transfer.358	/// - `to`: Recepient of transfered tokens.359	/// - `amount`: Amount of tokens to transfer.360	/// - `collection`: Collection that contains the token361	pub fn transfer(362		collection: &FungibleHandle<T>,363		from: &T::CrossAccountId,364		to: &T::CrossAccountId,365		amount: u128,366		nesting_budget: &dyn Budget,367	) -> DispatchResult {368		ensure!(amount > 0, <CommonError<T>>::ZeroTransferNotAllowed);369370		ensure!(371			collection.limits.transfers_enabled(),372			<CommonError<T>>::TransferNotAllowed,373		);374375		if collection.permissions.access() == AccessMode::AllowList {376			collection.check_allowlist(from)?;377			collection.check_allowlist(to)?;378		}379		<PalletCommon<T>>::ensure_correct_receiver(to)?;380381		let balance_from = <Balance<T>>::get((collection.id, from))382			.checked_sub(amount)383			.ok_or(<CommonError<T>>::TokenValueTooLow)?;384		let balance_to = if from != to {385			Some(386				<Balance<T>>::get((collection.id, to))387					.checked_add(amount)388					.ok_or(ArithmeticError::Overflow)?,389			)390		} else {391			None392		};393394		// =========395396		<PalletStructure<T>>::nest_if_sent_to_token(397			from.clone(),398			to,399			collection.id,400			TokenId::default(),401			nesting_budget,402		)?;403404		if let Some(balance_to) = balance_to {405			// from != to406			if balance_from == 0 {407				<Balance<T>>::remove((collection.id, from));408				<PalletStructure<T>>::unnest_if_nested(from, collection.id, TokenId::default());409			} else {410				<Balance<T>>::insert((collection.id, from), balance_from);411			}412			<Balance<T>>::insert((collection.id, to), balance_to);413		}414415		<PalletEvm<T>>::deposit_log(416			ERC20Events::Transfer {417				from: *from.as_eth(),418				to: *to.as_eth(),419				value: amount.into(),420			}421			.to_log(collection_id_to_address(collection.id)),422		);423		<PalletCommon<T>>::deposit_event(CommonEvent::Transfer(424			collection.id,425			TokenId::default(),426			from.clone(),427			to.clone(),428			amount,429		));430		Ok(())431	}432433	/// Minting tokens for multiple IDs.434	/// It is a utility function used in [`create_multiple_items`][`Pallet::create_multiple_items`]435	/// and [`create_multiple_items_foreign`][`Pallet::create_multiple_items_foreign`]436	pub fn create_multiple_items_common(437		collection: &FungibleHandle<T>,438		sender: &T::CrossAccountId,439		data: BTreeMap<T::CrossAccountId, u128>,440		nesting_budget: &dyn Budget,441	) -> DispatchResult {442		let total_supply = data443			.iter()444			.map(|(_, v)| *v)445			.try_fold(<TotalSupply<T>>::get(collection.id), |acc, v| {446				acc.checked_add(v)447			})448			.ok_or(ArithmeticError::Overflow)?;449450		for (to, _) in data.iter() {451			<PalletStructure<T>>::check_nesting(452				sender.clone(),453				to,454				collection.id,455				TokenId::default(),456				nesting_budget,457			)?;458		}459460		let updated_balances = data461			.into_iter()462			.map(|(user, amount)| {463				let updated_balance = <Balance<T>>::get((collection.id, &user))464					.checked_add(amount)465					.ok_or(ArithmeticError::Overflow)?;466				Ok((user, amount, updated_balance))467			})468			.collect::<Result<Vec<_>, DispatchError>>()?;469470		// =========471472		<TotalSupply<T>>::insert(collection.id, total_supply);473		for (user, amount, updated_balance) in updated_balances {474			<Balance<T>>::insert((collection.id, &user), updated_balance);475			<PalletStructure<T>>::nest_if_sent_to_token_unchecked(476				&user,477				collection.id,478				TokenId::default(),479			);480			<PalletEvm<T>>::deposit_log(481				ERC20Events::Transfer {482					from: H160::default(),483					to: *user.as_eth(),484					value: amount.into(),485				}486				.to_log(collection_id_to_address(collection.id)),487			);488			<PalletCommon<T>>::deposit_event(CommonEvent::ItemCreated(489				collection.id,490				TokenId::default(),491				user.clone(),492				amount,493			));494		}495496		Ok(())497	}498499	/// Minting tokens for multiple IDs.500	/// See [`create_item`][`Pallet::create_item`] for more details.501	pub fn create_multiple_items(502		collection: &FungibleHandle<T>,503		sender: &T::CrossAccountId,504		data: BTreeMap<T::CrossAccountId, u128>,505		nesting_budget: &dyn Budget,506	) -> DispatchResult {507		// Foreign collection check508		ensure!(!collection.flags.foreign, <CommonError<T>>::NoPermission);509510		if !collection.is_owner_or_admin(sender) {511			ensure!(512				collection.permissions.mint_mode(),513				<CommonError<T>>::PublicMintingNotAllowed514			);515			collection.check_allowlist(sender)?;516517			for (owner, _) in data.iter() {518				collection.check_allowlist(owner)?;519			}520		}521522		Self::create_multiple_items_common(collection, sender, data, nesting_budget)523	}524525	/// Minting tokens for multiple IDs.526	/// See [`create_item_foreign`][`Pallet::create_item_foreign`] for more details.527	pub fn create_multiple_items_foreign(528		collection: &FungibleHandle<T>,529		sender: &T::CrossAccountId,530		data: BTreeMap<T::CrossAccountId, u128>,531		nesting_budget: &dyn Budget,532	) -> DispatchResult {533		Self::create_multiple_items_common(collection, sender, data, nesting_budget)534	}535536	fn set_allowance_unchecked(537		collection: &FungibleHandle<T>,538		owner: &T::CrossAccountId,539		spender: &T::CrossAccountId,540		amount: u128,541	) {542		if amount == 0 {543			<Allowance<T>>::remove((collection.id, owner, spender));544		} else {545			<Allowance<T>>::insert((collection.id, owner, spender), amount);546		}547548		<PalletEvm<T>>::deposit_log(549			ERC20Events::Approval {550				owner: *owner.as_eth(),551				spender: *spender.as_eth(),552				value: amount.into(),553			}554			.to_log(collection_id_to_address(collection.id)),555		);556		<PalletCommon<T>>::deposit_event(CommonEvent::Approved(557			collection.id,558			TokenId(0),559			owner.clone(),560			spender.clone(),561			amount,562		));563	}564565	/// Set allowance for the spender to `transfer` or `burn` owner's tokens.566	///567	/// - `collection`: Collection that contains the token568	/// - `owner`: Owner of tokens that sets the allowance.569	/// - `spender`: Recipient of the allowance rights.570	/// - `amount`: Amount of tokens the spender is allowed to `transfer` or `burn`.571	pub fn set_allowance(572		collection: &FungibleHandle<T>,573		owner: &T::CrossAccountId,574		spender: &T::CrossAccountId,575		amount: u128,576	) -> DispatchResult {577		if collection.permissions.access() == AccessMode::AllowList {578			collection.check_allowlist(owner)?;579			collection.check_allowlist(spender)?;580		}581582		if <Balance<T>>::get((collection.id, owner)) < amount {583			ensure!(584				collection.ignores_owned_amount(owner),585				<CommonError<T>>::CantApproveMoreThanOwned586			);587		}588589		// =========590591		Self::set_allowance_unchecked(collection, owner, spender, amount);592		Ok(())593	}594595	/// Checks if a non-owner has (enough) allowance from the owner to perform operations on the tokens.596	/// Returns the expected remaining allowance - it should be set manually if the transaction proceeds.597	///598	/// - `collection`: Collection that contains the token.599	/// - `spender`: CrossAccountId who has the allowance rights.600	/// - `from`: The owner of the tokens who sets the allowance.601	/// - `amount`: Amount of tokens by which the allowance sholud be reduced.602	fn check_allowed(603		collection: &FungibleHandle<T>,604		spender: &T::CrossAccountId,605		from: &T::CrossAccountId,606		amount: u128,607		nesting_budget: &dyn Budget,608	) -> Result<Option<u128>, DispatchError> {609		if spender.conv_eq(from) {610			return Ok(None);611		}612		if collection.permissions.access() == AccessMode::AllowList {613			// `from`, `to` checked in [`transfer`]614			collection.check_allowlist(spender)?;615		}616		if let Some(source) = T::CrossTokenAddressMapping::address_to_token(from) {617			// TODO: should collection owner be allowed to perform this transfer?618			ensure!(619				<PalletStructure<T>>::check_indirectly_owned(620					spender.clone(),621					source.0,622					source.1,623					None,624					nesting_budget625				)?,626				<CommonError<T>>::ApprovedValueTooLow,627			);628			return Ok(None);629		}630		let allowance = <Allowance<T>>::get((collection.id, from, spender)).checked_sub(amount);631		if allowance.is_none() {632			ensure!(633				collection.ignores_allowance(spender),634				<CommonError<T>>::ApprovedValueTooLow635			);636		}637638		Ok(allowance)639	}640641	/// Transfer fungible tokens from one account to another.642	/// Same as the [`transfer`][`Pallet::transfer`] but spender doesn't needs to be an owner of the token pieces.643	/// The owner should set allowance for the spender to transfer pieces.644	///	See [`set_allowance`][`Pallet::set_allowance`] for more details.645646	pub fn transfer_from(647		collection: &FungibleHandle<T>,648		spender: &T::CrossAccountId,649		from: &T::CrossAccountId,650		to: &T::CrossAccountId,651		amount: u128,652		nesting_budget: &dyn Budget,653	) -> DispatchResult {654		let allowance = Self::check_allowed(collection, spender, from, amount, nesting_budget)?;655656		// =========657658		Self::transfer(collection, from, to, amount, nesting_budget)?;659		if let Some(allowance) = allowance {660			Self::set_allowance_unchecked(collection, from, spender, allowance);661		}662		Ok(())663	}664665	/// Burn fungible tokens from the account.666	///667	/// Same as the [`burn`][`Pallet::burn`] but spender doesn't need to be an owner of the tokens. The `from` should668	/// set allowance for the spender to burn tokens.669	/// See [`set_allowance`][`Pallet::set_allowance`] for more details.670	pub fn burn_from(671		collection: &FungibleHandle<T>,672		spender: &T::CrossAccountId,673		from: &T::CrossAccountId,674		amount: u128,675		nesting_budget: &dyn Budget,676	) -> DispatchResult {677		let allowance = Self::check_allowed(collection, spender, from, amount, nesting_budget)?;678679		// =========680681		Self::burn(collection, from, amount)?;682		if let Some(allowance) = allowance {683			Self::set_allowance_unchecked(collection, from, spender, allowance);684		}685		Ok(())686	}687688	///	Creates fungible token.689	///690	/// The sender should be the owner/admin of the collection or collection should be configured691	/// to allow public minting.692	///693	/// - `data`: Contains user who will become the owners of the tokens and amount694	///   of tokens he will receive.695	pub fn create_item(696		collection: &FungibleHandle<T>,697		sender: &T::CrossAccountId,698		data: CreateItemData<T>,699		nesting_budget: &dyn Budget,700	) -> DispatchResult {701		Self::create_multiple_items(702			collection,703			sender,704			[(data.0, data.1)].into_iter().collect(),705			nesting_budget,706		)707	}708709	///	Creates fungible token.710	///711	/// - `data`: Contains user who will become the owners of the tokens and amount712	///   of tokens he will receive.713	pub fn create_item_foreign(714		collection: &FungibleHandle<T>,715		sender: &T::CrossAccountId,716		data: CreateItemData<T>,717		nesting_budget: &dyn Budget,718	) -> DispatchResult {719		Self::create_multiple_items_foreign(720			collection,721			sender,722			[(data.0, data.1)].into_iter().collect(),723			nesting_budget,724		)725	}726727	/// Returns 10 tokens owners in no particular order728	///729	/// There is no direct way to get token holders in ascending order,730	/// since `iter_prefix` returns values in no particular order.731	/// Therefore, getting the 10 largest holders with a large value of holders732	/// can lead to impact memory allocation + sorting with  `n * log (n)`.733	pub fn token_owners(734		collection: CollectionId,735		_token: TokenId,736	) -> Option<Vec<T::CrossAccountId>> {737		let res: Vec<T::CrossAccountId> = <Balance<T>>::iter_prefix((collection,))738			.map(|(owner, _amount)| owner)739			.take(10)740			.collect();741742		if res.is_empty() {743			None744		} else {745			Some(res)746		}747	}748}