---
title: "Using Use"
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{Using Use}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r, include = FALSE}
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)
```

The `renv::use()` function can make it easier to define stand-alone R scripts
that include their R package requirements directly in the script itself.
For example:

```{r eval=FALSE}
# write down the set of packages required by this script
renv::use(
  "digest",         # use the latest-available version of digest
  "rlang@0.3.4"     # use an older release of rlang (installed from archive)
)

# use the requested packages
digest::digest(list(answer = 42))
```

Running a script with these contents will:

1. Automatically download the requested packages -- in this case,
   the latest release of `digest`, alongside `rlang 0.3.4`,

2. Install the requested packages (plus their recursive package dependencies) to
   a temporary library path,
   
3. Activate that library path, so that it's used subsequently in the script.

`renv::use()` can hence be a useful way of sharing standalone R scripts with
a set of specific package requirements. Running these scripts will ensure the
requested packages are automatically downloaded and installed.

In addition, you can also supply the path to a lockfile. For example:

```{r eval=FALSE}
# use a particular lockfile in the context of this script
renv::use(lockfile = "/path/to/renv.lock")

# the rest of this script will run with the packages as declared
# in that lockfile installed into a temporary library path
```

This can be useful in projects where you'd like to associate different lockfiles
with different documents -- for example, in a [blog][blogdown] or a website
where you'd like to associate a separate lockfile with each post. Once the
post is complete, you could use `renv::snapshot(lockfile = "/path/to/renv.lock")`
to "save" the state that was active while authoring that lockfile, and then use
`renv::use(lockfile = "/path/to/renv.lock")` in that document to ensure the blog
post is always run using that lockfile on future renders.


[blogdown]: https://bookdown.org/yihui/blogdown/
