I heard peope say make is slow and recursive make is harmful

[ljh]

I split my project into modules, eg. main, foo.
The main module calls foo which is shared object library.


If I change the foo.c (not the interface foo.h), 
only foo.c is compiled and foo is linked.


So, is not what people say a matter of project organization?




$ pwd
/home/ljh/Documents/hello_makefile_OutOfSRC/src
$ ls
foo  main  Makefile
$


$ tree --charset C
.
|-- foo
|   |-- foo.c
|   |-- foo.h
|   `-- Makefile
|-- main
|   |-- main.c
|   `-- Makefile
`-- Makefile


$ 


$ make 
make[1]: Entering directory 
'/home/ljh/Documents/hello_makefile_OutOfSRC/src/foo'
make[1]: Nothing to be done for 'all'.
make[1]: Leaving directory '/home/ljh/Documents/hello_makefile_OutOfSRC/src/foo'
make[1]: Entering directory 
'/home/ljh/Documents/hello_makefile_OutOfSRC/src/main'
make[1]: Nothing to be done for 'all'.
make[1]: Leaving directory 
'/home/ljh/Documents/hello_makefile_OutOfSRC/src/main'
$ 


$ touch foo/foo.c 


$ make 
make[1]: Entering directory 
'/home/ljh/Documents/hello_makefile_OutOfSRC/src/foo'
cc -fPIC  -g  -MMD -MP  -c -o 
/home/ljh/Documents/hello_makefile_OutOfSRC/src/build/foo/foo.o foo.c
cc -shared 
 -Wl,-rpath,/home/ljh/Documents/hello_makefile_OutOfSRC/src/build/bar 
-Wl,-rpath,'$ORIGIN/../lib' -Wl,-soname,libfoo.so.1 -fsanitize=address 
/home/ljh/Documents/hello_makefile_OutOfSRC/src/build/foo/foo.o  -o 
/home/ljh/Documents/hello_makefile_OutOfSRC/src/build/foo/foo
make[1]: Leaving directory '/home/ljh/Documents/hello_makefile_OutOfSRC/src/foo'
make[1]: Entering directory 
'/home/ljh/Documents/hello_makefile_OutOfSRC/src/main'
make[1]: Nothing to be done for 'all'.
make[1]: Leaving directory 
'/home/ljh/Documents/hello_makefile_OutOfSRC/src/main'
$