Object & changing target of CXXCOM

[Steven Allen]

Ok, I'm trying to get slicker and use more built in rules and rules checking
in cons.  This is probably a bit of a newbie question since I am pushing
into areas I've previously not explored.

My problem is I have a file dir/file.cpp that I want to compile and put it's
output in obj/file.o  

So

  Object $env "dir/file.cpp";

I can change CXXCOM as so 

  CXXCOM  => 'g++ %CFLAGS %_IFLAGS -c %< -o binary/%>:F.o',

This puts the .o file into the other directory just fine.  BUT cons doesn't
know that the target has changed from dir/file.o to binary/file.o and
*always* rebuild binary/file.o.  I can understand why, but I don't know how
to fix it.

Any clues.

Steve