# Deprecation of Features

From time to time we need to deprecate functionality, this is a guide as to how we implement deprecation.

## Types of deprecation

1. Misspelled function
2. Renamed function
3. Deprecated feature

## Period of maintenance

Toolkit retains deprecated features for a period of two releases. Thus features deprecated in 1.7.0 are removed in 1.9.0.

## Documentation

Use the `@deprecated` decorator with a comment and change the docstring to use the Sphinx deprecation syntax.

    @deprecated("Use util.run_fast() instead.")
    def run_slow():
        """Run slowly

        .. deprecated:: 1.9.0
           Use :func:`run_fast` instead.
        """
        run_fast()  # Call new function if possible

## Implementation

Deprecated features should call the new functionality if possible. This may not always be possible, such as the cases of drastic changes. But it is the preferred approach to reduce maintenance of the old code.

## Announcements

Note

This applies only to feature deprecation and renamed functions. Announcements for corrections are at the coders discretion.

1. On first release with deprecation highlight that the feature is deprecated in this release and explain reasons and alternate approaches.
2. On second relase warn that the feature will be removed in the next release.
3. On third release remove the feature and announce removal in the release announcements.

Thus by examples:

Translate Toolkit 1.9.0:
  The `run_slow` function has been deprecated and replaced by the faster and more correct `run_fast`. Users of `run_slow` are advised to migrate their code.
Translate Toolkit 1.10.0:
  The `run_slow` function has been deprecated and replaced by `run_fast` and will be removed in the next version. Users of `run_slow` are advised to migrate their code.
Translate Toolkit 1.11.0:
  The `run_slow` function has been removed, use `run_fast` instead.