Now I'm googling this and it looks like what you wrote would be a compiler error (assuming Foo.h was included into at least two files) unless the keyword inline

Now I'm googling this and it looks like what you wrote would be a compiler error (assuming Foo.h was included into at least two files) unless the keyword inline was used so that the same function could be defined multiple times. That clears up my confusion with your "default inline" statement.