# `Mob`
[🔗](https://github.com/genericjam/mob/blob/master/lib/mob.ex#L1)

Mob — BEAM-on-device mobile framework for Elixir.

OTP runs on the device. Screens are GenServers. The UI is rendered by
Compose (Android) and SwiftUI (iOS) via a thin NIF. No server required.

## Quick start

    defmodule MyApp.HomeScreen do
      use Mob.Screen

      def mount(_params, _session, socket) do
        {:ok, Mob.Socket.assign(socket, :title, "Hello, Mob!")}
      end

      def render(assigns) do
        %{
          type:  :column,
          props: %{padding: :space_md},
          children: [
            %{type: :text, props: %{text: assigns.title, text_size: :xl}, children: []}
          ]
        }
      end
    end

## Modules

- `Mob.App` — app entry point and navigation declaration
- `Mob.Screen` — screen behaviour and GenServer wrapper
- `Mob.Socket` — assigns and navigation API
- `Mob.Theme` — design token system
- `Mob.Renderer` — component tree serialisation
- `Mob.Test` — live device inspection and testing helpers

See the [Getting Started](getting_started.md) guide to create your first app,
and [Coming from Phoenix LiveView](coming_from_liveview.md) if you know
LiveView. See [Architecture & Prior Art](architecture.md) for how Mob compares
to LiveView Native, Elixir Desktop, React Native, Flutter, and native
development. AI agents: start at [Usage Rules](usage-rules.md), or
`https://hexdocs.pm/mob/llms.txt`.

# `assign`

# `assign`

# `data_dir`

```elixir
@spec data_dir() :: String.t()
```

A writable, app-private directory for runtime data — DB files, caches,
downloaded assets, anything you write at runtime.

On device this is `MOB_DATA_DIR`, set by the BEAM launcher to the platform's
persistent app-private location (iOS `NSDocumentDirectory`, Android
`getFilesDir()`). Off device (host/dev/tests) it falls back to `$HOME`, then
the current working directory. The directory is created if missing.

Use this — **not** `MOB_BEAMS_DIR`. `MOB_BEAMS_DIR` points inside the signed,
read-only `.app` bundle on iOS, so writing there fails with `:eperm`; it
happens to be writable on Android, which is how that trap stays hidden until
an app ships to iOS.

    path = Path.join(Mob.data_dir(), "my.db")

See `data_dir/1` for a created subdirectory.

# `data_dir`

```elixir
@spec data_dir(String.t()) :: String.t()
```

Like `data_dir/0` but returns (and creates) the `sub` directory beneath it,
e.g. `Mob.data_dir("audio_cache")`.

---

*Consult [api-reference.md](api-reference.md) for complete listing*