Address comments

examples/multi-token/mt/src/lib.rs

@@ -48,7 +48,6 @@ impl ExampleMTContract {
 
     #[init]
     pub fn new(owner_id: AccountId, metadata: MtContractMetadata) -> Self {
-        require!(!env::state_exists(), "Already initialized");
         metadata.assert_valid();
 
         Self {

near-contract-standards/src/multi_token/approval/approval_impl.rs

@@ -153,20 +153,14 @@ impl MultiTokenApproval for MultiToken {
         for (idx, (token_id, amount)) in token_ids.iter().zip(amounts).enumerate() {
             let by_owner = by_token.get(token_id).unwrap_or_default();
 
-            let grantee_to_approval = match by_owner.get(&owner_id) {
-                Some(grantee_to_approval) => grantee_to_approval,
-                None => return false,
+            let approval = match by_owner
+                .get(&owner_id)
+                .and_then(|grantee_to_approval| grantee_to_approval.get(&approved_account_id))
+            {
+                Some(approval) if approval.amount.eq(&amount.into()) => approval,
+                _ => return false,
             };
 
-            let approval = match grantee_to_approval.get(&approved_account_id) {
-                Some(approval) => approval,
-                None => return false,
-            };
-
-            if !approval.amount.eq(&amount.into()) {
-                return false;
-            }
-
             if let Some(given_approval) = approval_ids.get(idx) {
                 if !approval.approval_id.eq(given_approval) {
                     return false;

near-contract-standards/src/multi_token/core/core_impl.rs

@@ -1,5 +1,5 @@
 use near_sdk::borsh::{self, BorshDeserialize, BorshSerialize};
-use near_sdk::collections::{LookupMap, TreeMap, UnorderedMap, UnorderedSet};
+use near_sdk::collections::{LookupMap, UnorderedMap, UnorderedSet};
 use near_sdk::json_types::U128;
 use near_sdk::{
     assert_one_yocto, env, log, require, AccountId, Balance, BorshStorageKey, CryptoHash, Gas,
@@ -49,7 +49,7 @@ pub struct MultiToken {
     pub extra_storage_in_bytes_per_emission: StorageUsage,
 
     /// Owner of each token
-    pub owner_by_id: TreeMap<TokenId, AccountId>,
+    pub owner_by_id: UnorderedMap<TokenId, AccountId>,
 
     /// Total supply for each token
     pub total_supply: LookupMap<TokenId, Balance>,
@@ -124,7 +124,7 @@ impl MultiToken {
         let mut this = Self {
             owner_id,
             extra_storage_in_bytes_per_emission: 0,
-            owner_by_id: TreeMap::new(owner_by_id_prefix),
+            owner_by_id: UnorderedMap::new(owner_by_id_prefix),
             total_supply: LookupMap::new(StorageKey::TotalSupply { supply: 0 }),
             token_metadata_by_id: token_metadata_prefix.map(LookupMap::new),
             tokens_per_owner: enumeration_prefix.map(LookupMap::new),

near-contract-standards/src/multi_token/enumeration/enumeration_impl.rs

@@ -24,7 +24,7 @@ impl MultiTokenEnumeration for MultiToken {
             self.owner_by_id.len() as u128 >= start_index,
             "Out of bounds, please use a smaller from_index."
         );
-        let limit = limit.map(|v| v as usize).unwrap_or(usize::MAX);
+        let limit = limit.unwrap_or(u64::MAX);
         require!(limit != 0, "Limit cannot be 0");
 
         self.owner_by_id

near-contract-standards/src/multi_token/token.rs

@@ -18,9 +18,16 @@ pub struct Approval {
 // How Approvals are stored in the contract
 pub type ApprovalContainer = LookupMap<TokenId, HashMap<AccountId, HashMap<AccountId, Approval>>>;
 
-// Represents a temporary record of an Approval
-// that was removed from the ApprovalContainer but may be restored in case of rollback in XCC.
-// Values are (owner_id, approval_id, amount)
+// Represents a record of an Approval that has been temporarily added or removed 
+// from the ApprovalContainer during cross-contract calls (XCC).
+// This data is stored to facilitate possible rollback scenarios where the 
+// approval needs to be restored.
+//
+// The tuple contains the following elements:
+// - `AccountId`: The Account ID of the owner who initially granted the approval.
+// - `Approval`: A struct containing:
+//   - `amount`: The number of tokens that were initially approved for transfer.
+//   - `approval_id`: A unique identifier assigned to this specific approval.
 pub type ClearedApproval = (AccountId, Approval);
 
 /// Info on individual token