ianmcook commented on a change in pull request #9952:
URL: https://github.com/apache/arrow/pull/9952#discussion_r610784646
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File path: r/R/arrow-datum.R
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@@ -22,6 +22,7 @@
ArrowDatum <- R6Class("ArrowDatum", inherit = ArrowObject,
public = list(
cast = function(target_type, safe = TRUE, ...) {
+ target_type <- unmask_type_fun(enexpr(target_type)) %||% target_type
Review comment:
`{{x}}` is shorthand for `!!enquo(x)` which creates a quosure then
evaluates it. I don't think that works in this context. I tried some various
other approaches, e.g. just using `enoquo(x)`, using `eval(substitute(x))`,
etc. (which some of my earlier commits show the history of) but those failed to
handle all cases. In particular, we want to handle all these cases:
- `type` is a variable in the calling environment whose value is a
`DataType` object
- type` is a call to a function defined by the user that returns a
`DataType` object
- `type` is any arbitrary R expression that the user has wired up to return
a `DataType` object
- `type` is a call to a function in another package or in the user's
environment that masks the Arrow type function of the same name
The `%||% type` part of in `unmask_type_fun(enexpr(type)) %||% type` is
basically saying "if you tried to defuse `type` and evaluate in the arrow
package environment but that failed, then give up on the NSE approach and just
evaluate `type` in the standard way. That was important for enabling the first
three cases above to work.
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