git.delta.rocks / unique-network / refs/commits / c6354cf493a0

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		/// Setting approval for all is not allowed.131		SettingApprovalForAllNotAllowed,132	}133134	#[pallet::config]135	pub trait Config:136		frame_system::Config + pallet_common::Config + pallet_structure::Config + pallet_evm::Config137	{138		type WeightInfo: WeightInfo;139	}140141	#[pallet::pallet]142	#[pallet::generate_store(pub(super) trait Store)]143	pub struct Pallet<T>(_);144145	/// Total amount of fungible tokens inside a collection.146	#[pallet::storage]147	pub type TotalSupply<T: Config> =148		StorageMap<Hasher = Twox64Concat, Key = CollectionId, Value = u128, QueryKind = ValueQuery>;149150	/// Amount of tokens owned by an account inside a collection.151	#[pallet::storage]152	pub type Balance<T: Config> = StorageNMap<153		Key = (154			Key<Twox64Concat, CollectionId>,155			Key<Blake2_128Concat, T::CrossAccountId>,156		),157		Value = u128,158		QueryKind = ValueQuery,159	>;160161	/// Storage for assets delegated to a limited extent to other users.162	#[pallet::storage]163	pub type Allowance<T: Config> = StorageNMap<164		Key = (165			Key<Twox64Concat, CollectionId>,166			Key<Blake2_128, T::CrossAccountId>,167			Key<Blake2_128Concat, T::CrossAccountId>,168		),169		Value = u128,170		QueryKind = ValueQuery,171	>;172}173174/// Wrapper around untyped collection handle, asserting inner collection is of fungible type.175/// Required for interaction with Fungible collections, type safety and implementation [`solidity_interface`][`evm_coder::solidity_interface`].176pub struct FungibleHandle<T: Config>(pallet_common::CollectionHandle<T>);177178/// Implementation of methods required for dispatching during runtime.179impl<T: Config> FungibleHandle<T> {180	/// Casts [`CollectionHandle`][`pallet_common::CollectionHandle`] into [`FungibleHandle`].181	pub fn cast(inner: pallet_common::CollectionHandle<T>) -> Self {182		Self(inner)183	}184185	/// Casts [`FungibleHandle`] into [`CollectionHandle`][`pallet_common::CollectionHandle`].186	pub fn into_inner(self) -> pallet_common::CollectionHandle<T> {187		self.0188	}189	/// Returns a mutable reference to the internal [`CollectionHandle`][`pallet_common::CollectionHandle`].190	pub fn common_mut(&mut self) -> &mut pallet_common::CollectionHandle<T> {191		&mut self.0192	}193}194impl<T: Config> WithRecorder<T> for FungibleHandle<T> {195	fn recorder(&self) -> &pallet_evm_coder_substrate::SubstrateRecorder<T> {196		self.0.recorder()197	}198	fn into_recorder(self) -> pallet_evm_coder_substrate::SubstrateRecorder<T> {199		self.0.into_recorder()200	}201}202impl<T: Config> Deref for FungibleHandle<T> {203	type Target = pallet_common::CollectionHandle<T>;204205	fn deref(&self) -> &Self::Target {206		&self.0207	}208}209210/// Pallet implementation for fungible assets211impl<T: Config> Pallet<T> {212	/// Initializes the collection. Returns [CollectionId] on success, [DispatchError] otherwise.213	pub fn init_collection(214		owner: T::CrossAccountId,215		payer: T::CrossAccountId,216		data: CreateCollectionData<T::AccountId>,217		flags: CollectionFlags,218	) -> Result<CollectionId, DispatchError> {219		<PalletCommon<T>>::init_collection(owner, payer, data, flags)220	}221222	/// Initializes the collection with ForeignCollection flag. Returns [CollectionId] on success, [DispatchError] otherwise.223	pub fn init_foreign_collection(224		owner: T::CrossAccountId,225		payer: T::CrossAccountId,226		data: CreateCollectionData<T::AccountId>,227	) -> Result<CollectionId, DispatchError> {228		let id = <PalletCommon<T>>::init_collection(229			owner,230			payer,231			data,232			CollectionFlags {233				foreign: true,234				..Default::default()235			},236		)?;237		Ok(id)238	}239240	/// Destroys a collection.241	pub fn destroy_collection(242		collection: FungibleHandle<T>,243		sender: &T::CrossAccountId,244	) -> DispatchResult {245		let id = collection.id;246247		if Self::collection_has_tokens(id) {248			return Err(<CommonError<T>>::CantDestroyNotEmptyCollection.into());249		}250251		// =========252253		PalletCommon::destroy_collection(collection.0, sender)?;254255		<TotalSupply<T>>::remove(id);256		let _ = <Balance<T>>::clear_prefix((id,), u32::MAX, None);257		let _ = <Allowance<T>>::clear_prefix((id,), u32::MAX, None);258		Ok(())259	}260261	///Checks if collection has tokens. Return `true` if it has.262	fn collection_has_tokens(collection_id: CollectionId) -> bool {263		<TotalSupply<T>>::get(collection_id) != 0264	}265266	/// Burns the specified amount of the token. If the token balance267	/// or total supply is less than the given value,268	/// it will return [DispatchError].269	pub fn burn(270		collection: &FungibleHandle<T>,271		owner: &T::CrossAccountId,272		amount: u128,273	) -> DispatchResult {274		let total_supply = <TotalSupply<T>>::get(collection.id)275			.checked_sub(amount)276			.ok_or(<CommonError<T>>::TokenValueTooLow)?;277278		let balance = <Balance<T>>::get((collection.id, owner))279			.checked_sub(amount)280			.ok_or(<CommonError<T>>::TokenValueTooLow)?;281282		// Foreign collection check283		ensure!(!collection.flags.foreign, <CommonError<T>>::NoPermission);284285		if collection.permissions.access() == AccessMode::AllowList {286			collection.check_allowlist(owner)?;287		}288289		// =========290291		if balance == 0 {292			<Balance<T>>::remove((collection.id, owner));293			<PalletStructure<T>>::unnest_if_nested(owner, collection.id, TokenId::default());294		} else {295			<Balance<T>>::insert((collection.id, owner), balance);296		}297		<TotalSupply<T>>::insert(collection.id, total_supply);298299		<PalletEvm<T>>::deposit_log(300			ERC20Events::Transfer {301				from: *owner.as_eth(),302				to: H160::default(),303				value: amount.into(),304			}305			.to_log(collection_id_to_address(collection.id)),306		);307		<PalletCommon<T>>::deposit_event(CommonEvent::ItemDestroyed(308			collection.id,309			TokenId::default(),310			owner.clone(),311			amount,312		));313		Ok(())314	}315316	/// Burns the specified amount of the token.317	pub fn burn_foreign(318		collection: &FungibleHandle<T>,319		owner: &T::CrossAccountId,320		amount: u128,321	) -> DispatchResult {322		let total_supply = <TotalSupply<T>>::get(collection.id)323			.checked_sub(amount)324			.ok_or(<CommonError<T>>::TokenValueTooLow)?;325326		let balance = <Balance<T>>::get((collection.id, owner))327			.checked_sub(amount)328			.ok_or(<CommonError<T>>::TokenValueTooLow)?;329		// =========330331		if balance == 0 {332			<Balance<T>>::remove((collection.id, owner));333			<PalletStructure<T>>::unnest_if_nested(owner, collection.id, TokenId::default());334		} else {335			<Balance<T>>::insert((collection.id, owner), balance);336		}337		<TotalSupply<T>>::insert(collection.id, total_supply);338339		<PalletEvm<T>>::deposit_log(340			ERC20Events::Transfer {341				from: *owner.as_eth(),342				to: H160::default(),343				value: amount.into(),344			}345			.to_log(collection_id_to_address(collection.id)),346		);347		<PalletCommon<T>>::deposit_event(CommonEvent::ItemDestroyed(348			collection.id,349			TokenId::default(),350			owner.clone(),351			amount,352		));353		Ok(())354	}355356	/// Transfers the specified amount of tokens. Will check that357	/// the transfer is allowed for the token.358	///359	/// - `from`: Owner of tokens to transfer.360	/// - `to`: Recepient of transfered tokens.361	/// - `amount`: Amount of tokens to transfer.362	/// - `collection`: Collection that contains the token363	pub fn transfer(364		collection: &FungibleHandle<T>,365		from: &T::CrossAccountId,366		to: &T::CrossAccountId,367		amount: u128,368		nesting_budget: &dyn Budget,369	) -> DispatchResult {370		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 && amount != 0 {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		if let Some(balance_to) = balance_to {397			// from != to && amount != 0398399			<PalletStructure<T>>::nest_if_sent_to_token(400				from.clone(),401				to,402				collection.id,403				TokenId::default(),404				nesting_budget,405			)?;406407			if balance_from == 0 {408				<Balance<T>>::remove((collection.id, from));409				<PalletStructure<T>>::unnest_if_nested(from, collection.id, TokenId::default());410			} else {411				<Balance<T>>::insert((collection.id, from), balance_from);412			}413			<Balance<T>>::insert((collection.id, to), balance_to);414		}415416		<PalletEvm<T>>::deposit_log(417			ERC20Events::Transfer {418				from: *from.as_eth(),419				to: *to.as_eth(),420				value: amount.into(),421			}422			.to_log(collection_id_to_address(collection.id)),423		);424		<PalletCommon<T>>::deposit_event(CommonEvent::Transfer(425			collection.id,426			TokenId::default(),427			from.clone(),428			to.clone(),429			amount,430		));431		Ok(())432	}433434	/// Minting tokens for multiple IDs.435	/// It is a utility function used in [`create_multiple_items`][`Pallet::create_multiple_items`]436	/// and [`create_multiple_items_foreign`][`Pallet::create_multiple_items_foreign`]437	pub fn create_multiple_items_common(438		collection: &FungibleHandle<T>,439		sender: &T::CrossAccountId,440		data: BTreeMap<T::CrossAccountId, u128>,441		nesting_budget: &dyn Budget,442	) -> DispatchResult {443		let total_supply = data444			.iter()445			.map(|(_, v)| *v)446			.try_fold(<TotalSupply<T>>::get(collection.id), |acc, v| {447				acc.checked_add(v)448			})449			.ok_or(ArithmeticError::Overflow)?;450451		for (to, _) in data.iter() {452			<PalletStructure<T>>::check_nesting(453				sender.clone(),454				to,455				collection.id,456				TokenId::default(),457				nesting_budget,458			)?;459		}460461		let updated_balances = data462			.into_iter()463			.map(|(user, amount)| {464				let updated_balance = <Balance<T>>::get((collection.id, &user))465					.checked_add(amount)466					.ok_or(ArithmeticError::Overflow)?;467				Ok((user, amount, updated_balance))468			})469			.collect::<Result<Vec<_>, DispatchError>>()?;470471		// =========472473		<TotalSupply<T>>::insert(collection.id, total_supply);474		for (user, amount, updated_balance) in updated_balances {475			<Balance<T>>::insert((collection.id, &user), updated_balance);476			<PalletStructure<T>>::nest_if_sent_to_token_unchecked(477				&user,478				collection.id,479				TokenId::default(),480			);481			<PalletEvm<T>>::deposit_log(482				ERC20Events::Transfer {483					from: H160::default(),484					to: *user.as_eth(),485					value: amount.into(),486				}487				.to_log(collection_id_to_address(collection.id)),488			);489			<PalletCommon<T>>::deposit_event(CommonEvent::ItemCreated(490				collection.id,491				TokenId::default(),492				user.clone(),493				amount,494			));495		}496497		Ok(())498	}499500	/// Minting tokens for multiple IDs.501	/// See [`create_item`][`Pallet::create_item`] for more details.502	pub fn create_multiple_items(503		collection: &FungibleHandle<T>,504		sender: &T::CrossAccountId,505		data: BTreeMap<T::CrossAccountId, u128>,506		nesting_budget: &dyn Budget,507	) -> DispatchResult {508		// Foreign collection check509		ensure!(!collection.flags.foreign, <CommonError<T>>::NoPermission);510511		if !collection.is_owner_or_admin(sender) {512			ensure!(513				collection.permissions.mint_mode(),514				<CommonError<T>>::PublicMintingNotAllowed515			);516			collection.check_allowlist(sender)?;517518			for (owner, _) in data.iter() {519				collection.check_allowlist(owner)?;520			}521		}522523		Self::create_multiple_items_common(collection, sender, data, nesting_budget)524	}525526	/// Minting tokens for multiple IDs.527	/// See [`create_item_foreign`][`Pallet::create_item_foreign`] for more details.528	pub fn create_multiple_items_foreign(529		collection: &FungibleHandle<T>,530		sender: &T::CrossAccountId,531		data: BTreeMap<T::CrossAccountId, u128>,532		nesting_budget: &dyn Budget,533	) -> DispatchResult {534		Self::create_multiple_items_common(collection, sender, data, nesting_budget)535	}536537	fn set_allowance_unchecked(538		collection: &FungibleHandle<T>,539		owner: &T::CrossAccountId,540		spender: &T::CrossAccountId,541		amount: u128,542	) {543		if amount == 0 {544			<Allowance<T>>::remove((collection.id, owner, spender));545		} else {546			<Allowance<T>>::insert((collection.id, owner, spender), amount);547		}548549		<PalletEvm<T>>::deposit_log(550			ERC20Events::Approval {551				owner: *owner.as_eth(),552				spender: *spender.as_eth(),553				value: amount.into(),554			}555			.to_log(collection_id_to_address(collection.id)),556		);557		<PalletCommon<T>>::deposit_event(CommonEvent::Approved(558			collection.id,559			TokenId(0),560			owner.clone(),561			spender.clone(),562			amount,563		));564	}565566	/// Set allowance for the spender to `transfer` or `burn` owner's tokens.567	///568	/// - `collection`: Collection that contains the token569	/// - `owner`: Owner of tokens that sets the allowance.570	/// - `spender`: Recipient of the allowance rights.571	/// - `amount`: Amount of tokens the spender is allowed to `transfer` or `burn`.572	pub fn set_allowance(573		collection: &FungibleHandle<T>,574		owner: &T::CrossAccountId,575		spender: &T::CrossAccountId,576		amount: u128,577	) -> DispatchResult {578		if collection.permissions.access() == AccessMode::AllowList {579			collection.check_allowlist(owner)?;580			collection.check_allowlist(spender)?;581		}582583		if <Balance<T>>::get((collection.id, owner)) < amount {584			ensure!(585				collection.ignores_owned_amount(owner),586				<CommonError<T>>::CantApproveMoreThanOwned587			);588		}589590		// =========591592		Self::set_allowance_unchecked(collection, owner, spender, amount);593		Ok(())594	}595596	/// Checks if a non-owner has (enough) allowance from the owner to perform operations on the tokens.597	/// Returns the expected remaining allowance - it should be set manually if the transaction proceeds.598	///599	/// - `collection`: Collection that contains the token.600	/// - `spender`: CrossAccountId who has the allowance rights.601	/// - `from`: The owner of the tokens who sets the allowance.602	/// - `amount`: Amount of tokens by which the allowance sholud be reduced.603	fn check_allowed(604		collection: &FungibleHandle<T>,605		spender: &T::CrossAccountId,606		from: &T::CrossAccountId,607		amount: u128,608		nesting_budget: &dyn Budget,609	) -> Result<Option<u128>, DispatchError> {610		if spender.conv_eq(from) {611			return Ok(None);612		}613		if collection.permissions.access() == AccessMode::AllowList {614			// `from`, `to` checked in [`transfer`]615			collection.check_allowlist(spender)?;616		}617		if let Some(source) = T::CrossTokenAddressMapping::address_to_token(from) {618			// TODO: should collection owner be allowed to perform this transfer?619			ensure!(620				<PalletStructure<T>>::check_indirectly_owned(621					spender.clone(),622					source.0,623					source.1,624					None,625					nesting_budget626				)?,627				<CommonError<T>>::ApprovedValueTooLow,628			);629			return Ok(None);630		}631		let allowance = <Allowance<T>>::get((collection.id, from, spender)).checked_sub(amount);632		if allowance.is_none() {633			ensure!(634				collection.ignores_allowance(spender),635				<CommonError<T>>::ApprovedValueTooLow636			);637		}638639		Ok(allowance)640	}641642	/// Transfer fungible tokens from one account to another.643	/// Same as the [`transfer`][`Pallet::transfer`] but spender doesn't needs to be an owner of the token pieces.644	/// The owner should set allowance for the spender to transfer pieces.645	///	See [`set_allowance`][`Pallet::set_allowance`] for more details.646647	pub fn transfer_from(648		collection: &FungibleHandle<T>,649		spender: &T::CrossAccountId,650		from: &T::CrossAccountId,651		to: &T::CrossAccountId,652		amount: u128,653		nesting_budget: &dyn Budget,654	) -> DispatchResult {655		let allowance = Self::check_allowed(collection, spender, from, amount, nesting_budget)?;656657		// =========658659		Self::transfer(collection, from, to, amount, nesting_budget)?;660		if let Some(allowance) = allowance {661			Self::set_allowance_unchecked(collection, from, spender, allowance);662		}663		Ok(())664	}665666	/// Burn fungible tokens from the account.667	///668	/// Same as the [`burn`][`Pallet::burn`] but spender doesn't need to be an owner of the tokens. The `from` should669	/// set allowance for the spender to burn tokens.670	/// See [`set_allowance`][`Pallet::set_allowance`] for more details.671	pub fn burn_from(672		collection: &FungibleHandle<T>,673		spender: &T::CrossAccountId,674		from: &T::CrossAccountId,675		amount: u128,676		nesting_budget: &dyn Budget,677	) -> DispatchResult {678		let allowance = Self::check_allowed(collection, spender, from, amount, nesting_budget)?;679680		// =========681682		Self::burn(collection, from, amount)?;683		if let Some(allowance) = allowance {684			Self::set_allowance_unchecked(collection, from, spender, allowance);685		}686		Ok(())687	}688689	///	Creates fungible token.690	///691	/// The sender should be the owner/admin of the collection or collection should be configured692	/// to allow public minting.693	///694	/// - `data`: Contains user who will become the owners of the tokens and amount695	///   of tokens he will receive.696	pub fn create_item(697		collection: &FungibleHandle<T>,698		sender: &T::CrossAccountId,699		data: CreateItemData<T>,700		nesting_budget: &dyn Budget,701	) -> DispatchResult {702		Self::create_multiple_items(703			collection,704			sender,705			[(data.0, data.1)].into_iter().collect(),706			nesting_budget,707		)708	}709710	///	Creates fungible token.711	///712	/// - `data`: Contains user who will become the owners of the tokens and amount713	///   of tokens he will receive.714	pub fn create_item_foreign(715		collection: &FungibleHandle<T>,716		sender: &T::CrossAccountId,717		data: CreateItemData<T>,718		nesting_budget: &dyn Budget,719	) -> DispatchResult {720		Self::create_multiple_items_foreign(721			collection,722			sender,723			[(data.0, data.1)].into_iter().collect(),724			nesting_budget,725		)726	}727728	/// Returns 10 tokens owners in no particular order729	///730	/// There is no direct way to get token holders in ascending order,731	/// since `iter_prefix` returns values in no particular order.732	/// Therefore, getting the 10 largest holders with a large value of holders733	/// can lead to impact memory allocation + sorting with  `n * log (n)`.734	pub fn token_owners(735		collection: CollectionId,736		_token: TokenId,737	) -> Option<Vec<T::CrossAccountId>> {738		let res: Vec<T::CrossAccountId> = <Balance<T>>::iter_prefix((collection,))739			.map(|(owner, _amount)| owner)740			.take(10)741			.collect();742743		if res.is_empty() {744			None745		} else {746			Some(res)747		}748	}749}