Move common move command verification into a shared function

contracts/src/main/kotlin/contracts/Cash.kt

@@ -130,14 +130,7 @@ class Cash : Contract {
                         (inputAmount == outputAmount + amountExitingLedger)
             }
 
-            // Now check the digital signatures on the move command. Every input has an owning public key, and we must
+            verifyMoveCommand<Commands.Move>(inputs, tx)
-            // see a signature from each of those keys. The actual signatures have been verified against the transaction
-            // data by the platform before execution.
-            val owningPubKeys = inputs.map { it.owner }.toSet()
-            val keysThatSigned = tx.commands.requireSingleCommand<Commands.Move>().signers.toSet()
-            requireThat {
-                "the owning keys are the same as the signing keys" by keysThatSigned.containsAll(owningPubKeys)
-            }
         }
     }
 

core/src/main/kotlin/core/ContractsDSL.kt

@@ -81,3 +81,20 @@ fun List<AuthenticatedObject<CommandData>>.getTimestampByName(vararg names: Stri
         return null
 }
 
+/**
+ * Simple functionality for verifying a move command. Verifies that each input has a signature from its owning key.
+ *
+ * @param T the type of the move command
+ */
+@Throws(IllegalArgumentException::class)
+// TODO: Can we have a common Move command for all contracts and avoid the reified type parameter here?
+inline fun <reified T : CommandData> verifyMoveCommands(inputs: List<OwnableState>, tx: TransactionForVerification) {
+    // Now check the digital signatures on the move command. Every input has an owning public key, and we must
+    // see a signature from each of those keys. The actual signatures have been verified against the transaction
+    // data by the platform before execution.
+    val owningPubKeys = inputs.map { it.owner }.toSet()
+    val keysThatSigned = tx.commands.requireSingleCommand<T>().signers.toSet()
+    requireThat {
+        "the owning keys are the same as the signing keys" by keysThatSigned.containsAll(owningPubKeys)
+    }
+}