Reusing a checkout
==================

Motivation
----------

At times, it can be useful to have a single checkout as your
sandbox for working on multiple branches. Some possible reasons
for this include:

 * saving disk space when the working tree is large
 * developing in a fixed location.

In many cases, working tree disk usage swamps the size of the
``.bzr`` directory. If you want to work on multiple branches
but can't afford the overhead of a full working tree for each,
reusing a checkout across multiples branches is the way to go.

On other occasions, the location of your sandbox might be
configured into numerous development and testing tools. Once
again, reusing a checkout across multiple branches can help.


Changing where a branch is bound to
-----------------------------------

To change where a checkout is bound to, follow these steps:

 1. Make sure that any local changes have been committed
    centrally so that no work is lost.

 2. Use the ``bind`` command giving the URL of the new
    remote branch you wish to work on.

 3. Make your checkout a copy of the desired branch by using
    the ``update`` command followed by the ``revert`` command.

Note that simply binding to a new branch and running ``update``
merges in your local changes, both committed and uncommitted. You need
to decide whether to keep them or not by running either ``revert``
or ``commit``.

An alternative to the bind+update recipe is using the ``switch``
command. This is basically the same as removing the existing
branch and running ``checkout`` again on the new location, except
that any uncommitted changes in your tree are merged in.

Note: As ``switch`` can potentially throw away committed changes in
order to make a checkout an accurate cache of a different bound branch,
it will fail by design if there are changes which have been committed
locally but are not yet committed to the most recently bound branch.
To truly abandon these changes, use the ``--force`` option.


Switching a lightweight checkout
--------------------------------

With a lightweight checkout, there are no local commits and ``switch``
effectively changes which branch the working tree is associated with.
One possible setup is to use a lightweight checkout in combination
with a local tree-less repository. This lets you switch what you
are working on with ease. For example::

  bzr init-repo --no-trees PROJECT
  cd PROJECT
  bzr branch bzr+ssh://centralhost/srv/bzr/PROJECT/trunk
  bzr checkout --lightweight trunk my-sandbox
  cd my-sandbox
  (hack away)

Note that trunk in this example will have a ``.bzr`` directory within it
but there will be no working tree there as the branch was created in
a tree-less repository. You can grab or create as many branches as you
need there and switch between them as required. For example::

  (assuming in my-sandbox)
  bzr branch bzr+ssh://centralhost/srv/bzr/PROJECT/PROJECT-1.0 ../PROJECT-1.0
  bzr switch ../PROJECT-1.0
  (fix bug in 1.0)
  bzr commit -m "blah, blah blah"
  bzr switch ../trunk
  (go back to working on the trunk)

Note: The branches may be local only or they may be bound to
remote ones (by creating them with ``checkout`` or by using ``bind``
after creating them with ``branch``).
