shiny/man/isolate.Rd

\name{isolate}
\alias{isolate}
\title{Create a non-reactive scope for an expression}
\usage{
  isolate(expr)
}
\arguments{
  \item{expr}{An expression that can access reactive values
  or functions.}
}
\description{
  Executes the given expression in a scope where reactive
  values or functions can be read, but they cannot cause
  the reactive scope of the caller to be re-evaluated when
  they change.
}
\details{
  Ordinarily, the simple act of reading a reactive value
  causes a relationship to be established between the
  caller and the reactive value, where a change to the
  reactive value will cause the caller to re-execute. (The
  same applies for the act of getting a reactive function's
  value.) The \code{isolate} function lets you read a
  reactive value or function without establishing this
  relationship.

  The expression given to \code{isolate()} is evaluated in
  the calling environment. This means that if you assign a
  variable inside the \code{isolate()}, its value will be
  visible outside of the \code{isolate()}. If you want to
  avoid this, you can use \code{\link{local}()} inside the
  \code{isolate()}.

  This function can also be useful for calling reactive
  functions at the console, which can be useful for
  debugging. To do so, simply wrap the functino calls with
  \code{isolate()}.
}
\examples{
\dontrun{
observe(function() {
  input$saveButton  # Do take a dependency on input$saveButton

  # isolate a simple expression
  data <- get(isolate(input$dataset))  # No dependency on input$dataset
  writeToDatabase(data)
})

observe(function() {
  input$saveButton  # Do take a dependency on input$saveButton

  # isolate a whole block
  data <- isolate({
    a <- input$valueA   # No dependency on input$valueA or input$valueB
    b <- input$valueB
    c(a=a, b=b)
  })
  writeToDatabase(data)
})

observe(function() {
  x <- 1
  # x outside of isolate() is affected
  isolate(x <- 2)
  print(x) # 2

  y <- 1
  # Use local() to avoid affecting calling environment
  isolate(local(y <- 2))
  print(y) # 1
})

}

# Can also use isolate to call reactive functions from the R console
values <- reactiveValues(A=1)
fun <- reactive(function() as.character(values$A))
isolate(fun())
# "1"

# isolate also works if the reactive function accesses values from the
# input object, like input$x
}