(v2) Generic model

[aymanbagabas]

This proposal removes all program options and, instead, define them directly on the Program struct. This also changes the API and implement this proposal #1136

type Program[T any] struct {
	Input  io.Reader
	Output io.Writer
	Env    []string
	Init   func() (T, Cmd)
	Filter func(T, Msg) Msg
	Update func(T, Msg) (T, Cmd)
	View   func(T) Frame
	Model T

	// DontCatchPanics is a flag that determines whether or not the program should
	// catch panics.
	DontCatchPanics bool

	// IgnoreSignals is a flag that determines whether or not the program should
	// ignore signals.
	IgnoreSignals bool

	// FPS is the frames per second we should set on the renderer, if
	// applicable,
	FPS int

	// Profile is the color profile of the terminal. Use [Profile] to set it.
	Profile colorprofile.Profile // the terminal color profile
}

[aymanbagabas]

Here's an example of rewriting the cursor-style example using this API

package main

import (
	"fmt"
	"os"

	tea "github.com/charmbracelet/bubbletea/v2"
)

type model struct {
	shape tea.CursorShape
	blink bool
}

func (m model) describeCursor() string {
	var adj, noun string

	if m.blink {
		adj = "blinking"
	} else {
		adj = "steady"
	}

	switch m.shape {
	case tea.CursorBlock:
		noun = "block"
	case tea.CursorUnderline:
		noun = "underline"
	case tea.CursorBar:
		noun = "bar"
	}

	return fmt.Sprintf("%s %s", adj, noun)
}

func initialModel() (model, tea.Cmd) {
	m := model{blink: true}
	return m, nil
}

func updateModel(m model, msg tea.Msg) (model, tea.Cmd) {
	switch msg := msg.(type) {
	case tea.KeyPressMsg:
		switch msg.String() {
		case "ctrl+q", "q":
			return m, tea.Quit
		case "h", "left":
			if m.shape == tea.CursorBlock && m.blink {
				break
			}
			if m.blink {
				m.shape--
			}
			m.blink = !m.blink
		case "l", "right":
			if m.shape == tea.CursorBar && !m.blink {
				break
			}
			if !m.blink {
				m.shape++
			}
			m.blink = !m.blink
		}
	}
	return m, nil
}

func viewModel(m model) fmt.Stringer {
	f := tea.NewFrame("Press left/right to change the cursor style, q or ctrl+c to quit." +
		"\n\n" +
		"  <- This is the cursor (a " + m.describeCursor() + ")")
	f.Cursor = tea.NewCursor(0, 2)
	f.Cursor.Shape = m.shape
	f.Cursor.Blink = m.blink
	return f
}

func main() {
	p := tea.Program[model]{
		Init:   initialModel,
		Update: updateModel,
		View:   viewModel,
	}
	if err := p.Run(); err != nil {
		fmt.Fprintf(os.Stderr, "Error: %v", err)
		os.Exit(1)
	}
}

[dolmen]

This line would me much simpler (and less runtime cost in every call to Update, View) if Model[T] was a struct instead of an interface. See #1136 (comment)

[dolmen]

The NewProgram implementation wraps the Update and View functions (which are called frequently in the render loop) in a costly way. See my proposal for an alternate representation of Model[T] in #1136 (comment).