ensurer is a utility package for R that provides a simple and
light-weight mechanism for ensuring certain aspects of values at runtime.
As an example, a query to a database or the scraping of a website might not
return valid data, where "validity" can refer to a number of conditions. It
might be a positive or certain number of records; that all cases are
complete; that some column is weekly increasing; or simply that the result is
a data.frame.
If one does not deal with these ambiguities and risks appropriately, some resulting errors may be hard to track down or may even go unnoticed. It is desirable to get an error immediately when a value does not have the correct type or does not satisfy certain criteria.
"Ensuring values" is here meant as a "contract", or a set of conditions, such
that if a value does not comply an error is raised instantly. An ensuring
contract (a function) is created with ensures_that (ideal for
multiple use or readability with complex contracts).
It is also possible to ensure properties on the fly using
ensure_that (ideal for simple, one-time contracts).
Using the magrittr pipe %>% greatly improves semantics of the
functionality provided by this package, but it is not necessary.
This package is not meant as a substitute for unit testing, and great
packages for this already exist, e.g. testthat by Hadley Wickham. The
ensurer package is meant as a simple and ideal tool for scripts or
programs where runtime conditions may break the functionality, and where
errors should be raised as soon and clear as possible.
For a more thorough introduction, see vignette(ensurer).