Remove ErrMsg and ModelAssertionErr

examples/http/main.go

@@ -15,11 +15,12 @@ import (
 const url = "https://charm.sh/"
 
 type Model struct {
-	Status int
+	status int
-	Error  error
+	err    error
 }
 
 type statusMsg int
+type errMsg error
 
 func main() {
 	p := tea.NewProgram(initialize, update, view, nil)
@@ -33,7 +34,10 @@ func initialize() (tea.Model, tea.Cmd) {
 }
 
 func update(msg tea.Msg, model tea.Model) (tea.Model, tea.Cmd) {
-	m, _ := model.(Model)
+	m, ok := model.(Model)
+	if !ok {
+		return Model{err: errors.New("could not perform assertion on model during update")}, nil
+	}
 
 	switch msg := msg.(type) {
 
@@ -50,12 +54,11 @@ func update(msg tea.Msg, model tea.Model) (tea.Model, tea.Cmd) {
 		}
 
 	case statusMsg:
-		m.Status = int(msg)
+		m.status = int(msg)
 		return m, tea.Quit
 
-	case tea.ErrMsg:
+	case errMsg:
-		// TODO: get the error out of tea.ErrMsg less hackily
+		m.err = msg
-		m.Error = errors.New(msg.Error())
 		return m, nil
 
 	default:
@@ -66,10 +69,10 @@ func update(msg tea.Msg, model tea.Model) (tea.Model, tea.Cmd) {
 func view(model tea.Model) string {
 	m, _ := model.(Model)
 	s := fmt.Sprintf("Checking %s...", url)
-	if m.Error != nil {
+	if m.err != nil {
-		s += fmt.Sprintf("something went wrong: %s", m.Error)
+		s += fmt.Sprintf("something went wrong: %s", m.err)
-	} else if m.Status != 0 {
+	} else if m.status != 0 {
-		s += fmt.Sprintf("%d %s", m.Status, http.StatusText(m.Status))
+		s += fmt.Sprintf("%d %s", m.status, http.StatusText(m.status))
 	}
 	return s
 }
@@ -80,7 +83,7 @@ func checkServer() tea.Msg {
 	}
 	res, err := c.Get(url)
 	if err != nil {
-		return tea.NewErrMsg(err.Error())
+		return errMsg(err)
 	}
 	return statusMsg(res.StatusCode)
 }

examples/input/main.go

@@ -12,15 +12,14 @@ import (
 )
 
 type Model struct {
-	Input input.Model
+	textInput input.Model
-	Error error
+	err       error
 }
 
 type tickMsg struct{}
+type errMsg error
 
 func main() {
-	tea.UseSysLog("tea")
-
 	p := tea.NewProgram(
 		initialize,
 		update,
@@ -38,8 +37,8 @@ func initialize() (tea.Model, tea.Cmd) {
 	inputModel.Placeholder = "Pikachu"
 
 	return Model{
-		Input: inputModel,
+		textInput: inputModel,
-		Error: nil,
+		err:       nil,
 	}, nil
 }
 
@@ -50,8 +49,9 @@ func update(msg tea.Msg, model tea.Model) (tea.Model, tea.Cmd) {
 		// When we encounter errors in Update we simply add the error to the
 		// model so we can handle it in the view. We could also return a command
 		// that does something else with the error, like logs it via IO.
-		m.Error = errors.New("could not perform assertion on model")
+		return Model{
-		return m, nil
+			err: errors.New("could not perform assertion on model in update"),
+		}, nil
 	}
 
 	switch msg := msg.(type) {
@@ -64,12 +64,12 @@ func update(msg tea.Msg, model tea.Model) (tea.Model, tea.Cmd) {
 		}
 
 	// We handle errors just like any other message
-	case tea.ErrMsg:
+	case errMsg:
-		m.Error = msg
+		m.err = msg
 		return m, nil
 	}
 
-	m.Input, cmd = input.Update(msg, m.Input)
+	m.textInput, cmd = input.Update(msg, m.textInput)
 	return m, cmd
 }
 
@@ -79,7 +79,7 @@ func subscriptions(model tea.Model) tea.Subs {
 		// it the model it expects.
 		"input": func(model tea.Model) tea.Msg {
 			m, _ := model.(Model)
-			return input.Blink(m.Input)
+			return input.Blink(m.textInput)
 		},
 	}
 }
@@ -88,12 +88,12 @@ func view(model tea.Model) string {
 	m, ok := model.(Model)
 	if !ok {
 		return "Oh no: could not perform assertion on model."
-	} else if m.Error != nil {
+	} else if m.err != nil {
-		return fmt.Sprintf("Uh oh: %s", m.Error)
+		return fmt.Sprintf("Uh oh: %s", m.err)
 	}
 	return fmt.Sprintf(
 		"What’s your favorite Pokémon?\n\n%s\n\n%s",
-		input.View(m.Input),
+		input.View(m.textInput),
 		"(esc to quit)",
 	)
 }

tea.go

@@ -1,7 +1,6 @@
 package tea
 
 import (
-	"errors"
 	"io"
 	"os"
 	"strings"
@@ -94,32 +93,6 @@ type Program struct {
 	subscriptions Subscriptions
 }
 
-// ErrMsg is just a regular message containing an error. We handle it in Update
-// just like a regular message by case switching. Of course, the developer
-// could also define her own errors as well.
-type ErrMsg struct {
-	error
-}
-
-// String implements String() on the error interface for ErrMsg
-func (e ErrMsg) String() string {
-	return e.Error()
-}
-
-// NewErrMsg is a convenience function for creating a generic ErrMsg
-func NewErrMsg(s string) ErrMsg {
-	return ErrMsg{errors.New(s)}
-}
-
-// NewErrMsgFromErr is a convenience function for creating an ErrMsg from an
-// existing error
-func NewErrMsgFromErr(e error) ErrMsg {
-	return ErrMsg{e}
-}
-
-// ModelAssertionErr can be used when a model assertion didn't go as planned
-var ModelAssertionErr = NewErrMsg("could not perform assertion on model")
-
 // Quit is a command that tells the program to exit
 func Quit() Msg {
 	return quitMsg{}