How to make a formula for dcast()?

Suppose you want to go back from heatlong (in long format) to wide format. You need to use dcast() for that.

This function has an argument called formula. The value for this argument is a formula in the following format:

name of column that will be used to make the rows in wide format ~ name of column that will be used to make the columns in wide format

Which of the options below will transform heatlong back in wide format?