Implement `InspectEnumerable` for Uniques (#9117)

* implement InspectEnumerable in pallet_uniques

* use `iter_keys` and `iter_key_prefix`

* return an iterator instead of constructing a vec

* update comments

* additional warning about storage reads

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

substrate/frame/support/src/traits/tokens/nonfungible.rs

@@ -61,14 +61,12 @@ pub trait Inspect<AccountId> {
 
 /// Interface for enumerating assets in existence or owned by a given account over a collection
 /// of NFTs.
-///
-/// WARNING: These may be a heavy operations. Do not use when execution time is limited.
 pub trait InspectEnumerable<AccountId>: Inspect<AccountId> {
-	/// Returns the instances of an asset `class` in existence.
-	fn instances() -> Vec<Self::InstanceId>;
+	/// Returns an iterator of the instances of an asset `class` in existence.
+	fn instances() -> Box<dyn Iterator<Item = Self::InstanceId>>;
 
-	/// Returns the asset instances of all classes owned by `who`.
-	fn owned(who: &AccountId) -> Vec<Self::InstanceId>;
+	/// Returns an iterator of the asset instances of all classes owned by `who`.
+	fn owned(who: &AccountId) -> Box<dyn Iterator<Item = Self::InstanceId>>;
 }
 
 /// Trait for providing an interface for NFT-like assets which may be minted, burned and/or have
@@ -148,10 +146,10 @@ impl<
 	A: Get<<F as nonfungibles::Inspect<AccountId>>::ClassId>,
 	AccountId,
 > InspectEnumerable<AccountId> for ItemOf<F, A, AccountId> {
-	fn instances() -> Vec<Self::InstanceId> {
+	fn instances() -> Box<dyn Iterator<Item = Self::InstanceId>> {
 		<F as nonfungibles::InspectEnumerable<AccountId>>::instances(&A::get())
 	}
-	fn owned(who: &AccountId) -> Vec<Self::InstanceId> {
+	fn owned(who: &AccountId) -> Box<dyn Iterator<Item = Self::InstanceId>> {
 		<F as nonfungibles::InspectEnumerable<AccountId>>::owned_in_class(&A::get(), who)
 	}
 }

substrate/frame/support/src/traits/tokens/nonfungibles.rs

@@ -95,20 +95,18 @@ pub trait Inspect<AccountId> {
 
 /// Interface for enumerating assets in existence or owned by a given account over many collections
 /// of NFTs.
-///
-/// WARNING: These may be a heavy operations. Do not use when execution time is limited.
 pub trait InspectEnumerable<AccountId>: Inspect<AccountId> {
-	/// Returns the asset classes in existence.
-	fn classes() -> Vec<Self::ClassId>;
+	/// Returns an iterator of the asset classes in existence.
+	fn classes() -> Box<dyn Iterator<Item = Self::ClassId>>;
 
-	/// Returns the instances of an asset `class` in existence.
-	fn instances(class: &Self::ClassId) -> Vec<Self::InstanceId>;
+	/// Returns an iterator of the instances of an asset `class` in existence.
+	fn instances(class: &Self::ClassId) -> Box<dyn Iterator<Item = Self::InstanceId>>;
 
-	/// Returns the asset instances of all classes owned by `who`.
-	fn owned(who: &AccountId) -> Vec<(Self::ClassId, Self::InstanceId)>;
+	/// Returns an iterator of the asset instances of all classes owned by `who`.
+	fn owned(who: &AccountId) -> Box<dyn Iterator<Item = (Self::ClassId, Self::InstanceId)>>;
 
-	/// Returns the asset instances of `class` owned by `who`.
-	fn owned_in_class(class: &Self::ClassId, who: &AccountId) -> Vec<Self::InstanceId>;
+	/// Returns an iterator of the asset instances of `class` owned by `who`.
+	fn owned_in_class(class: &Self::ClassId, who: &AccountId) -> Box<dyn Iterator<Item = Self::InstanceId>>;
 }
 
 /// Trait for providing an interface for multiple classes of NFT-like assets which may be minted,

substrate/frame/uniques/src/impl_nonfungibles.rs

@@ -19,7 +19,7 @@
 
 use super::*;
 use sp_std::convert::TryFrom;
-use frame_support::traits::tokens::nonfungibles::{Inspect, Mutate, Transfer};
+use frame_support::traits::tokens::nonfungibles::{Inspect, InspectEnumerable, Mutate, Transfer};
 use frame_support::BoundedSlice;
 use sp_runtime::DispatchResult;
 
@@ -106,3 +106,33 @@ impl<T: Config<I>, I: 'static> Transfer<T::AccountId> for Pallet<T, I> {
 		Self::do_transfer(class.clone(), instance.clone(), destination.clone(), |_, _| Ok(()))
 	}
 }
+
+impl<T: Config<I>, I: 'static> InspectEnumerable<T::AccountId> for Pallet<T, I> {
+	/// Returns an iterator of the asset classes in existence.
+	///
+	/// NOTE: iterating this list invokes a storage read per item.
+	fn classes() -> Box<dyn Iterator<Item = Self::ClassId>> {
+		Box::new(ClassMetadataOf::<T, I>::iter_keys())
+	}
+
+	/// Returns an iterator of the instances of an asset `class` in existence.
+	///
+	/// NOTE: iterating this list invokes a storage read per item.
+	fn instances(class: &Self::ClassId) -> Box<dyn Iterator<Item = Self::InstanceId>> {
+		Box::new(InstanceMetadataOf::<T, I>::iter_key_prefix(class))
+	}
+
+	/// Returns an iterator of the asset instances of all classes owned by `who`.
+	///
+	/// NOTE: iterating this list invokes a storage read per item.
+	fn owned(who: &T::AccountId) -> Box<dyn Iterator<Item = (Self::ClassId, Self::InstanceId)>> {
+		Box::new(Account::<T, I>::iter_key_prefix((who,)))
+	}
+
+	/// Returns an iterator of the asset instances of `class` owned by `who`.
+	///
+	/// NOTE: iterating this list invokes a storage read per item.
+	fn owned_in_class(class: &Self::ClassId, who: &T::AccountId) -> Box<dyn Iterator<Item = Self::InstanceId>> {
+		Box::new(Account::<T, I>::iter_key_prefix((who, class)))
+	}
+}