Non-fungible token traits (#8993)

* Non-fungible token traits

* Docs

* Fixes

* Implement non-fungible trait for Uniques

* Update frame/uniques/src/impl_nonfungibles.rs

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>

* Update frame/uniques/src/impl_nonfungibles.rs

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>

Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>

substrate/frame/uniques/src/functions.rs

@@ -0,0 +1,115 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2017-2021 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Various pieces of common functionality.
+
+use super::*;
+use frame_support::{ensure, traits::Get};
+use sp_runtime::{DispatchResult, DispatchError};
+
+impl<T: Config<I>, I: 'static> Pallet<T, I> {
+	pub(crate) fn do_transfer(
+		class: T::ClassId,
+		instance: T::InstanceId,
+		dest: T::AccountId,
+		with_details: impl FnOnce(
+			&ClassDetailsFor<T, I>,
+			&mut InstanceDetailsFor<T, I>,
+		) -> DispatchResult,
+	) -> DispatchResult {
+		let class_details = Class::<T, I>::get(&class).ok_or(Error::<T, I>::Unknown)?;
+		ensure!(!class_details.is_frozen, Error::<T, I>::Frozen);
+
+		let mut details = Asset::<T, I>::get(&class, &instance).ok_or(Error::<T, I>::Unknown)?;
+		ensure!(!details.is_frozen, Error::<T, I>::Frozen);
+		with_details(&class_details, &mut details)?;
+
+		Account::<T, I>::remove((&details.owner, &class, &instance));
+		Account::<T, I>::insert((&dest, &class, &instance), ());
+		let origin = details.owner;
+		details.owner = dest;
+		Asset::<T, I>::insert(&class, &instance, &details);
+
+		Self::deposit_event(Event::Transferred(class, instance, origin, details.owner));
+		Ok(())
+	}
+
+	pub(super) fn do_mint(
+		class: T::ClassId,
+		instance: T::InstanceId,
+		owner: T::AccountId,
+		with_details: impl FnOnce(
+			&ClassDetailsFor<T, I>,
+		) -> DispatchResult,
+	) -> DispatchResult {
+		ensure!(!Asset::<T, I>::contains_key(class, instance), Error::<T, I>::AlreadyExists);
+
+		Class::<T, I>::try_mutate(&class, |maybe_class_details| -> DispatchResult {
+			let class_details = maybe_class_details.as_mut().ok_or(Error::<T, I>::Unknown)?;
+
+			with_details(&class_details)?;
+
+			let instances = class_details.instances.checked_add(1)
+				.ok_or(ArithmeticError::Overflow)?;
+			class_details.instances = instances;
+
+			let deposit = match class_details.free_holding {
+				true => Zero::zero(),
+				false => T::InstanceDeposit::get(),
+			};
+			T::Currency::reserve(&class_details.owner, deposit)?;
+			class_details.total_deposit += deposit;
+
+			let owner = owner.clone();
+			Account::<T, I>::insert((&owner, &class, &instance), ());
+			let details = InstanceDetails { owner, approved: None, is_frozen: false, deposit};
+			Asset::<T, I>::insert(&class, &instance, details);
+			Ok(())
+		})?;
+
+		Self::deposit_event(Event::Issued(class, instance, owner));
+		Ok(())
+	}
+
+	pub(super) fn do_burn(
+		class: T::ClassId,
+		instance: T::InstanceId,
+		with_details: impl FnOnce(
+			&ClassDetailsFor<T, I>,
+			&InstanceDetailsFor<T, I>,
+		) -> DispatchResult,
+	) -> DispatchResult {
+		let owner = Class::<T, I>::try_mutate(&class, |maybe_class_details| -> Result<T::AccountId, DispatchError> {
+			let class_details = maybe_class_details.as_mut().ok_or(Error::<T, I>::Unknown)?;
+			let details = Asset::<T, I>::get(&class, &instance)
+				.ok_or(Error::<T, I>::Unknown)?;
+			with_details(&class_details, &details)?;
+
+			// Return the deposit.
+			T::Currency::unreserve(&class_details.owner, details.deposit);
+			class_details.total_deposit.saturating_reduce(details.deposit);
+			class_details.instances.saturating_dec();
+			Ok(details.owner)
+		})?;
+
+		Asset::<T, I>::remove(&class, &instance);
+		Account::<T, I>::remove((&owner, &class, &instance));
+
+		Self::deposit_event(Event::Burned(class, instance, owner));
+		Ok(())
+	}
+}