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ARROW-15193: [R][Documentation] Update R binding documentation #12075

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ARROW-15193: [R][Documentation] Update R binding documentation #12075

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25 changes: 19 additions & 6 deletions r/vignettes/developers/bindings.Rmd
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Expand Up @@ -194,15 +194,22 @@ adding to the `nse_funcs` list in `arrow/r/R/dplyr-functions.R`. Here is how
this might look for `startsWith()`:

```{r, eval = FALSE}
nse_funcs$startsWith <- function(x, prefix) {
register_binding("startsWith", function(x, prefix) {
Expression$create(
"starts_with",
x,
options = list(pattern = prefix)
)
}
})
```

In the source files, all the `register_binding()` calls are wrapped in functions
that are called on package load. These are separated into files based on
subject matter (e.g., `R/dplyr-funcs-math.R`, `R/dplyr-funcs-string.R`): find the
closest analog to the function whose binding is being defined and define the
new binding in a similar location. For example, the binding for `startsWith()`
is registered in `dplyr-funcs-string.R` next to the binding for `endsWith()`.

Hint: you can use `call_function()` to call a compute function directly from R.
This might be useful if you want to experiment with a compute function while
you're writing bindings for it, e.g.
Expand All @@ -217,9 +224,15 @@ call_function(

## Step 4 - Run (and potentially add to) your tests.

In the process of implementing the function, you may end up implementing more
tests, for example if you discover unusual edge cases. This is fine - add them
to the ones you wrote originally, and run them all. If they pass, you're done!
Submit a PR. If you've modified the C++ code in the
In the process of implementing the function, you will need at least one test
to make sure that your binding works and that future changes to the Arrow R
package don't break it! Bindings are tested in files that correspond to
the file in which they were defined (e.g., `startsWith()` is tested in
`tests/testthat/test-dplyr-funcs-string.R`) next to the tests for `endsWith()`.

You may end up implementing more tests, for example if you discover unusual
edge cases. This is fine - add them to the ones you wrote originally,
and run them all. If they pass, you're done and you can submit a PR.
If you've modified the C++ code in the
R package (for example, when hooking up a binding to its options class), you
should make sure to run `arrow/r/lint.sh` to lint the code.