Instruction member function (#8801)

sdk/src/instruction.rs

@@ -201,6 +201,26 @@ impl CompiledInstruction {
     pub fn program_id<'a>(&self, program_ids: &'a [Pubkey]) -> &'a Pubkey {
         &program_ids[self.program_id_index as usize]
     }
+
+    /// Visit each unique instruction account index once
+    pub fn visit_each_account(
+        &self,
+        work: &mut dyn FnMut(usize, usize) -> Result<(), InstructionError>,
+    ) -> Result<(), InstructionError> {
+        let mut unique_index = 0;
+        'root: for (i, account_index) in self.accounts.iter().enumerate() {
+            // Note: This is an O(n^2) algorithm,
+            // but performed on a very small slice and requires no heap allocations
+            for account_index_before in self.accounts[..i].iter() {
+                if account_index_before == account_index {
+                    continue 'root; // skip dups
+                }
+            }
+            work(unique_index, *account_index as usize)?;
+            unique_index += 1;
+        }
+        Ok(())
+    }
 }
 
 #[cfg(test)]
@@ -236,4 +256,27 @@ mod test {
         assert!(metas[1].is_signer);
         assert_eq!(metas[1].pubkey, signer_pubkey);
     }
+
+    #[test]
+    fn test_visit_each_account() {
+        let do_work = |accounts: &[u8]| -> (usize, usize) {
+            let mut unique_total = 0;
+            let mut account_total = 0;
+            let mut work = |unique_index: usize, account_index: usize| {
+                unique_total += unique_index;
+                account_total += account_index;
+                Ok(())
+            };
+            let instruction = CompiledInstruction::new(0, &[0], accounts.to_vec());
+            instruction.visit_each_account(&mut work).unwrap();
+
+            (unique_total, account_total)
+        };
+
+        assert_eq!((6, 6), do_work(&[0, 1, 2, 3]));
+        assert_eq!((6, 6), do_work(&[0, 1, 1, 2, 3]));
+        assert_eq!((6, 6), do_work(&[0, 1, 2, 3, 3]));
+        assert_eq!((6, 6), do_work(&[0, 0, 1, 1, 2, 2, 3, 3]));
+        assert_eq!((0, 2), do_work(&[2, 2]));
+    }
 }