> ## Documentation Index
> Fetch the complete documentation index at: https://docs.refactron.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# class_to_dataclass

> Promote pure data-holder classes (trivial __init__) to @dataclass.

**Transform ID:** `class_to_dataclass`
**Language:** Python

## What it does

Detects classes whose `__init__` method only does `self.<name> = <name>` assignments and rewrites them as `@dataclass`. Each former init parameter becomes a typed field (`Any` when the original parameter has no annotation).

## Detector pattern

The detector at `src/analyze/detectors/python/class-init-only.ts` walks `ClassDef` nodes, accepts only those with a single `__init__` method, and verifies every body statement is an `Assign(targets=[Attribute(self, name)], value=Name(name))` shape.

## Preconditions

1. The class has exactly one method, and it is `__init__`.
2. The `__init__` body is purely `self.<name> = <name>` lines (no defaults, no transformations like `self.x = x * 2`).
3. The class has **no `__slots__`** declaration.
4. The class does **not inherit** from a parent with a custom `__init__`.
5. Init parameter names match the assignment target names (no `self.public = _private` redirection).

## Before / after

<CodeGroup>
  ```python before.py theme={null}
  class User:
      def __init__(self, id, name, email):
          self.id = id
          self.name = name
          self.email = email


  class Address:
      def __init__(self, street, city, zip):
          self.street = street
          self.city = city
          self.zip = zip
  ```

  ```python after.py theme={null}
  from dataclasses import dataclass
  from typing import Any


  @dataclass
  class User:
      id: Any
      name: Any
      email: Any


  @dataclass
  class Address:
      street: Any
      city: Any
      zip: Any
  ```
</CodeGroup>

## Edge cases handled

* Adds `from dataclasses import dataclass` and `from typing import Any` if missing.
* Preserves class docstrings and decorators that precede the class.
* Multiple convertible classes per file are all converted in one pass.

## Edge cases NOT handled (skip via precondition)

* Class has any method besides `__init__` (the transform refuses to promote — a dataclass with custom methods is fine in principle, but inferring `eq`/`hash`/`repr` interactions safely is out of scope for v0.2).
* Init body contains expressions (`self.id = id * 2`, `self.full_name = first + " " + last`).
* Init has default arguments (`def __init__(self, x=0)`) — supported by dataclass via `field(default=…)` but not auto-inferred here.
* Class uses `__slots__`.