git: Make the work tree reflect only a subpath of the whole tree -

i checkout whole branch, work inside specific directory of branch. therefore sort of "dive in" whole tree , make work tree reflect subdirectory chose. e.g.:

"master" tree   dir1/     file1     file2   dir2/     file3  work-dir tree   .git   file1   file2 

my guess this:

git checkout master:dir1/ 

however, doesn't work , reports error:

fatal: cannot switch branch non-commit 'master:dir1/' 

is possible?

note: don't want use submodules because don't want slice repo unrelated pieces. subtree merge, far can tell, helps me synchronize 2 separate directories similar structures different histories. want modify original objects in repo , able merge them , forth , retain history.

it's not possible. can use cd dir1 , git still work there, allowing use git add file1 instead of git add dir1/file1 etc.