Control "prevent.inplace" via an option, not a setDT argument.

R/as.data.table.R

@@ -66,7 +66,11 @@ as.data.table.matrix = function(x, keep.rownames=FALSE, key=NULL, ...) {
     for (i in ic) value[[i]] <- as.vector(x[, i])       # to drop any row.names that would otherwise be retained inside every column of the data.table
   }
   col_labels = dimnames(x)[[2L]]
-  setDT(value, set.allow.inplace.attrib=FALSE)
+
+  orig.opt <- options(data.table.prevent.inplace=TRUE)
+  on.exit(options(orig.opt))
+  setDT(value)
+
   if (length(col_labels) == ncols) {
     if (any(empty <- !nzchar(col_labels)))
       col_labels[empty] = paste0("V", ic[empty])
@@ -196,7 +200,13 @@ as.data.table.list = function(x,
   if (any(vnames==".SD")) stop("A column may not be called .SD. That has special meaning.")
   if (check.names) vnames = make.names(vnames, unique=TRUE)
   setattr(ans, "names", vnames)
-  setDT(ans, key=key, set.allow.inplace.attrib=FALSE) # copy ensured above; also, setDT handles naming
+
+  if (is.null(getOption("data.table.allow.inplace"))) { # not an internal call 
+    orig.opt <- options(data.table.prevent.inplace=FALSE)
+    on.exit(options(orig.opt))
+  }
+
+  setDT(ans, key=key) # copy ensured above; also, setDT handles naming
   if (length(origListNames)==length(ans)) setattr(ans, "names", origListNames)  # PR 3854 and tests 2058.15-17
   ans
 }

R/data.table.R

@@ -51,6 +51,12 @@ null.data.table = function() {
 
 data.table = function(..., keep.rownames=FALSE, check.names=FALSE, key=NULL, stringsAsFactors=FALSE)
 {
+  if (is.null(getOption("data.table.prevent.inplace"))) {
+    # need to add an explicit option, for a nested call to as.list.data.table that calls setDT
+    orig.opt <- options(data.table.prevent.inplace=FALSE)
+    on.exit(options(orig.opt))
+  }
+
   # NOTE: It may be faster in some circumstances for users to create a data.table by creating a list l
   #       first, and then setattr(l,"class",c("data.table","data.frame")) and forgo checking.
   x = list(...)   # list() doesn't copy named inputs as from R >= 3.1.0 (a very welcome change)
@@ -2708,8 +2714,7 @@ setDF = function(x, rownames=NULL) {
   invisible(x)
 }
 
-setDT = function(x, keep.rownames=FALSE, key=NULL, check.names=FALSE,
-                 set.allow.inplace.attrib=TRUE) {
+setDT = function(x, keep.rownames=FALSE, key=NULL, check.names=FALSE) {
   name = substitute(x)
   if (is.name(name)) {
     home = function(x, env) {
@@ -2748,7 +2753,7 @@ setDT = function(x, keep.rownames=FALSE, key=NULL, check.names=FALSE,
       x[, (nm[1L]) := rn]
       setcolorder(x, nm)
     }
-    if(set.allow.inplace.attrib)
+    if(getOption("data.table.prevent.inplace", default=TRUE))
       setattr(x, "allow.assign.inplace", FALSE)
   } else if (is.list(x) && length(x)==1L && is.matrix(x[[1L]])) {
     # a single list(matrix) is unambiguous and depended on by some revdeps, #3581
@@ -2785,7 +2790,7 @@ setDT = function(x, keep.rownames=FALSE, key=NULL, check.names=FALSE,
     setattr(x,"row.names",.set_row_names(n_range[2L]))
     setattr(x,"class",c("data.table","data.frame"))
     setalloccol(x)
-    if(set.allow.inplace.attrib)
+    if(getOption("data.table.prevent.inplace", default=TRUE))
       setattr(x, "allow.assign.inplace", FALSE)
   } else {
     stop("Argument 'x' to 'setDT' should be a 'list', 'data.frame' or 'data.table'")