Add isolate function for accessing reactives non-reactively

man/isolate.Rd

@@ -0,0 +1,50 @@
+\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.
+}
+\examples{
+\dontrun{
+observer(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)
+})
+
+observer(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)
+})
+}
+}
+