Added the argcheck method the the devicecmd struct

peripheral/devices/cdash_display.go

@@ -21,17 +21,28 @@ var CDashDisplay = Device{
 			Identifier: newWindowCMDID,
 			Name:       "new-window",
 			Desc:       "Creates a new window - pass the window name and dimensions",
+			ArgCheck:   createWindowArgCheck,
 			Fn:         createWindow,
 		},
 		"destroy-window": {
 			Identifier: destroyWindowCMDID,
 			Name:       "destroy-window",
 			Desc:       "Destroys a window by its ID",
+			ArgCheck:   destroyWindowArgCheck,
 			Fn:         destroyWindow,
 		},
 	},
 }
 
+func createWindowArgCheck(args []string) error {
+	if len(args) != 5 {
+		return fmt.Errorf("wrong parameters, got %d, want %d. "+
+			"Command asks for: x0 y0 width height title", len(args), 5)
+	}
+
+	return nil
+}
+
 func createWindow(dCMD *DeviceCMD, args []string) (types.Command, []byte, error) {
 	// Parse the command
 	// x0, y0, width, height, title # add other decorations later on
@@ -45,9 +56,9 @@ func createWindow(dCMD *DeviceCMD, args []string) (types.Command, []byte, error)
 		Title  [32]byte
 	}
 
-	if len(args) != 5 {
-		return 0, []byte{}, fmt.Errorf("wrong parameters, got %d, want %d. "+
-			"Command asks for: x0 y0 width height title", len(args), 5)
+	err := dCMD.ArgCheck(args)
+	if err != nil {
+		return 0, []byte{}, err
 	}
 
 	x0, err := strconv.ParseInt(args[0], 10, 0)
@@ -83,6 +94,15 @@ func createWindow(dCMD *DeviceCMD, args []string) (types.Command, []byte, error)
 	return dCMD.GetIdentifier(), bytes, nil
 }
 
+func destroyWindowArgCheck(args []string) error {
+	if len(args) != 1 {
+		return fmt.Errorf("wrong parameters, got %d, want %d. "+
+			"Command asks for: winID", len(args), 1)
+	}
+
+	return nil
+}
+
 func destroyWindow(dCMD *DeviceCMD, args []string) (types.Command, []byte, error) {
 	// Parse the command
 	fmt.Printf("%s command called: %+v\n", dCMD.GetName(), args)

peripheral/devices/devices.go

@@ -44,12 +44,17 @@ type DeviceCMDPayload struct {
 // types in the REPL - or however this will be used
 type DeviceCMDFn func(dCMD *DeviceCMD, args []string) (types.Command, []byte, error)
 
+// ArgCheckFn is a function to check the arguments passed. Returns nil or the error
+// in the passed arguments
+type ArgCheckFn func(args []string) error
+
 type DeviceCMD struct {
 	Identifier types.Command
 	Name       string
 	Desc       string
 	Header     DeviceCMDHeader
 	Data       DeviceCMDPayload
+	ArgCheck   ArgCheckFn
 	Fn         DeviceCMDFn
 }