HEAD, Checkout, Switch, Detached HEAD

What Is HEAD?

HEAD is a pointer representing the current position of the current worktree.

Normal state:

HEAD
 ↓
feature/camera
 ↓
Commit C

In other words, HEAD points to a branch, and the branch points to a commit.

A new commit:

A ─ B ─ C ─ D
            ↑ feature/camera
            ↑ HEAD

What Is Checkout?

The essence of checkout is:

Materializing the file state of a particular commit in the current worktree

Changing branches changes the following together.

• HEAD
• Index
• Actual files in the worktree

Historically:

git checkout feature/camera

Today, separating the commands by purpose makes them easier to understand.

git switch feature/camera      # Switch branches
git restore Camera.cpp         # Restore a file

What Happens When You Switch with Uncommitted Changes?

If Git can preserve them safely, your changes can come along with you.

However, Git stops if the changes conflict with files on the target branch and could be overwritten.

Your local changes would be overwritten...

Your options at that point are:

• Commit
• Stash
• Discard changes with restore

One reason to use worktrees is to reduce the need for these branch switches.

Detached HEAD

Normal:

HEAD → feature/camera → Commit C

Detached:

HEAD → Commit C

You are looking directly at a commit without going through a branch.

Uses:

• Inspect an older commit
• Build a specific version
• Temporarily inspect a remote branch’s state
• Experiment

Example:

git fetch origin
git switch --detach origin/feature/avatar

This lets you inspect the latest state of a remote branch pushed by someone else without creating a local branch.

If you want to make changes and continue development, create a local branch.

git switch -c feature/avatar --track origin/feature/avatar

Detached HEAD Does Not Mean Viewing All Branches at Once

A worktree always has exactly one HEAD.

To simply read content on another branch, you can avoid checkout with:

git show feature/a:Source/Camera.cpp

This also lets you inspect the file.