How to let R know a function is not an S3 method?

问题

If I define a function called

log.foo = function(foo){
  log(foo)
}

then R will think it is a S3 method. How can I tell R log.foo() is not the S3 method for the class foo. (In fact, class foo does not exist.)

Or do I just have to rename my function?

来源：https://stackoverflow.com/questions/23377869/how-to-let-r-know-a-function-is-not-an-s3-method