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* Start v1.9.0 release candidate * Check-in revdep results * `yarn build` (GitHub Actions) * Sync package version (GitHub Actions) * `yarn build` (GitHub Actions) * ran revdepcheck on cloud. 2 errors reported. Both seem like false positives * Fix R CMD check note about Rd links targets missing package anchors --------- Co-authored-by: cpsievert <cpsievert@users.noreply.github.com> Co-authored-by: Barret Schloerke <barret@posit.co> Co-authored-by: schloerke <schloerke@users.noreply.github.com>
94 lines
3.0 KiB
R
94 lines
3.0 KiB
R
% Generated by roxygen2: do not edit by hand
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% Please edit documentation in R/reactives.R
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\name{reactive}
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\alias{reactive}
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\alias{is.reactive}
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\title{Create a reactive expression}
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\usage{
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reactive(
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x,
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env = parent.frame(),
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quoted = FALSE,
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...,
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label = NULL,
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domain = getDefaultReactiveDomain(),
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..stacktraceon = TRUE
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)
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is.reactive(x)
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}
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\arguments{
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\item{x}{For \code{is.reactive()}, an object to test. For \code{reactive()}, an
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expression. When passing in a \code{\link[rlang:defusing-advanced]{rlang::quo()}}sure with \code{reactive()},
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remember to use \code{\link[rlang:inject]{rlang::inject()}} to distinguish that you are passing in
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the content of your quosure, not the expression of the quosure.}
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\item{env}{The parent environment for the reactive expression. By default,
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this is the calling environment, the same as when defining an ordinary
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non-reactive expression. If \code{x} is a quosure and \code{quoted} is \code{TRUE},
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then \code{env} is ignored.}
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\item{quoted}{If it is \code{TRUE}, then the \code{\link[=quote]{quote()}}ed value of \code{x}
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will be used when \code{x} is evaluated. If \code{x} is a quosure and you
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would like to use its expression as a value for \code{x}, then you must set
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\code{quoted} to \code{TRUE}.}
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\item{...}{Not used.}
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\item{label}{A label for the reactive expression, useful for debugging.}
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\item{domain}{See \link{domains}.}
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\item{..stacktraceon}{Advanced use only. For stack manipulation purposes; see
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\code{\link[=stacktrace]{stacktrace()}}.}
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}
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\value{
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a function, wrapped in a S3 class "reactive"
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}
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\description{
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Wraps a normal expression to create a reactive expression. Conceptually, a
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reactive expression is a expression whose result will change over time.
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}
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\details{
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Reactive expressions are expressions that can read reactive values and call
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other reactive expressions. Whenever a reactive value changes, any reactive
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expressions that depended on it are marked as "invalidated" and will
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automatically re-execute if necessary. If a reactive expression is marked as
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invalidated, any other reactive expressions that recently called it are also
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marked as invalidated. In this way, invalidations ripple through the
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expressions that depend on each other.
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See the \href{https://shiny.rstudio.com/tutorial/}{Shiny tutorial} for
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more information about reactive expressions.
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}
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\examples{
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library(rlang)
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values <- reactiveValues(A=1)
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reactiveB <- reactive({
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values$A + 1
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})
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# View the values from the R console with isolate()
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isolate(reactiveB())
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# 2
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# To store expressions for later conversion to reactive, use quote()
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myquo <- rlang::quo(values$A + 2)
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# Unexpected value! Sending a quosure directly will not work as expected.
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reactiveC <- reactive(myquo)
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# We'd hope for `3`, but instead we get the quosure that was supplied.
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isolate(reactiveC())
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# Instead, the quosure should be `rlang::inject()`ed
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reactiveD <- rlang::inject(reactive(!!myquo))
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isolate(reactiveD())
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# 3
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# (Legacy) Can use quoted expressions
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expr <- quote({ values$A + 3 })
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reactiveE <- reactive(expr, quoted = TRUE)
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isolate(reactiveE())
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# 4
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}
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