use factory pattern

Author: ben-schwen

R/fread.R

@@ -1,36 +1,36 @@
 # nocov start
-# S3 generic for reopening connections in binary mode
-reopen_connection = function(con, description, ...) {
-  UseMethod("reopen_connection")
+# S3 generic that returns a function to open connections in binary mode
+connection_opener = function(con, ...) {
+  UseMethod("connection_opener")
 }
 
-reopen_connection.default = function(con, description, ...) {
+connection_opener.default = function(con, ...) {
   con_class = class1(con)
   stopf("Don't know how to reopen connection type '%s'. Need a connection opened in binary mode to continue.", con_class)
 }
 
-reopen_connection.file = function(con, description, ...) {
-  file(description, "rb")
+connection_opener.file = function(con, ...) {
+  function(description) file(description, "rb", ...)
 }
 
-reopen_connection.gzfile = function(con, description, ...) {
-  gzfile(description, "rb")
+connection_opener.gzfile = function(con, ...) {
+  function(description) gzfile(description, "rb", ...)
 }
 
-reopen_connection.bzfile = function(con, description, ...) {
-  bzfile(description, "rb")
+connection_opener.bzfile = function(con, ...) {
+  function(description) bzfile(description, "rb", ...)
 }
 
-reopen_connection.url = function(con, description, ...) {
-  url(description, "rb")
+connection_opener.url = function(con, ...) {
+  function(description) url(description, "rb", ...)
 }
 
-reopen_connection.unz = function(con, description, ...) {
-  unz(description, "rb")
+connection_opener.unz = function(con, ...) {
+  function(description) unz(description, "rb", ...)
 }
 
-reopen_connection.pipe = function(con, description, ...) {
-  pipe(description, "rb")
+connection_opener.pipe = function(con, ...) {
+  function(description) pipe(description, "rb", ...)
 }
 # nocov end
 
@@ -146,7 +146,7 @@ yaml=FALSE, tmpdir=tempdir(), tz="UTC")
 
     if (needs_reopen) {
       close(input)
-      input = reopen_connection(input, con_summary$description)
+      input = connection_opener(input)(con_summary$description)
       close_con = input
     } else if (!con_open) {
       open(input, "rb")

man/connection_opener.Rd

@@ -0,0 +1,33 @@
+\name{connection_opener}
+\alias{connection_opener}
+\title{ Create a function to open connections in binary mode }
+\description{
+  S3 generic that returns a function to open a connection in binary read mode. Used internally by \code{fread}. Exported so packages with custom connection classes can define methods.
+}
+\usage{
+connection_opener(con, ...)
+}
+\arguments{
+  \item{con}{ A connection object. }
+  \item{...}{ Additional arguments passed to the connection constructor. }
+}
+\details{
+  Returns a function that accepts a description argument and opens a connection in binary read mode (\code{"rb"}). Methods are provided for \code{file}, \code{gzfile}, \code{bzfile}, \code{url}, \code{unz} and \code{pipe} connections.
+
+  To support custom connection types with \code{fread}, define a method for your connection class that returns an opener function.
+}
+\value{
+  A function that accepts a description argument and returns a connection object opened in binary read mode.
+}
+\examples{
+\dontrun{
+# Define a method for a custom connection class
+connection_opener.my_con = function(con, ...) {
+  function(description) my_con(description, mode = "rb", ...)
+}
+}
+}
+\seealso{
+  \code{\link{fread}}
+}
+\keyword{ data }