DIY_GIT_in_Python/how_to/Change_21.md

• tag: Generalize HEAD to refs

As part of implementing tag, we'll generalize the way we handle HEAD. If you think about it, HEAD and tags are similar. They are both ways for ugit to attach a name to an OID. In case of HEAD, the name is hardcoded by ugit; in case of tags, the name will be provided by the user. It makes sense to handle them similarly in data.py.

In data.py, let's extend the function set_HEAD and get_HEAD to update_ref and get_ref. "Ref" is a short for reference, and that's the name Git uses. The function will now accept the name of the ref and write/read it as a file under .ugit directory. Logically, a ref is a named pointer to an object.

The important change is in data.py. The rest of the changes just rename some functions:

- get_HEAD()    ->   get_ref('HEAD')
- set_HEAD(oid) ->   update_ref('HEAD', oid)

Note that we didn't change any behaviour of ugit here, this is purely refactoring.