'isolate' builtin; refs https://github.com/nim-lang/RFCs/issues/244 (#15011)

lib/std/isolation.nim

@@ -0,0 +1,31 @@
+#
+#
+#            Nim's Runtime Library
+#        (c) Copyright 2020 Nim contributors
+#
+#    See the file "copying.txt", included in this
+#    distribution, for details about the copyright.
+#
+
+## This module implements the `Isolated[T]` type for
+## safe construction of isolated subgraphs that can be
+## passed efficiently to different channels and threads.
+
+type
+  Isolated*[T] = object ## Isolated data can only be moved, not copied.
+    value: T
+
+proc `=`*[T](dest: var Isolated[T]; src: Isolated[T]) {.error.}
+
+proc `=sink`*[T](dest: var Isolated[T]; src: Isolated[T]) {.inline.} =
+  # delegate to value's sink operation
+  `=sink`(dest.value, src.value)
+
+proc `=destroy`*[T](dest: var Isolated[T]) {.inline.} =
+  # delegate to value's destroy operation
+  `=destroy`(dest.value)
+
+func isolate*[T](value: sink T): Isolated[T] {.magic: "Isolate".}
+  ## Create an isolated subgraph from the expression `value`.
+  ## Please read https://github.com/nim-lang/RFCs/issues/244
+  ## for more details.