Merge remote-tracking branch 'nim-lang/devel' into emscripten-support

1 files changed, 31 insertions, 0 deletions

diff --git a/lib/pure/asyncdispatch.nim b/lib/pure/asyncdispatch.nim
index f49388b17..292296d35 100644
--- a/lib/pure/asyncdispatch.nim
+++ b/lib/pure/asyncdispatch.nim
@@ -145,6 +145,8 @@ type
   Future*[T] = ref object of FutureBase ## Typed future.
     value: T ## Stored value
 
+  FutureVar*[T] = distinct Future[T]
+
 {.deprecated: [PFutureBase: FutureBase, PFuture: Future].}
 
 
@@ -162,6 +164,19 @@ proc newFuture*[T](fromProc: string = "unspecified"): Future[T] =
     result.fromProc = fromProc
     currentID.inc()
 
+proc newFutureVar*[T](fromProc = "unspecified"): FutureVar[T] =
+  ## Create a new ``FutureVar``. This Future type is ideally suited for
+  ## situations where you want to avoid unnecessary allocations of Futures.
+  ##
+  ## Specifying ``fromProc``, which is a string specifying the name of the proc
+  ## that this future belongs to, is a good habit as it helps with debugging.
+  result = FutureVar[T](newFuture[T](fromProc))
+
+proc clean*[T](future: FutureVar[T]) =
+  ## Resets the ``finished`` status of ``future``.
+  Future[T](future).finished = false
+  Future[T](future).error = nil
+
 proc checkFinished[T](future: Future[T]) =
   when not defined(release):
     if future.finished:
@@ -194,6 +209,15 @@ proc complete*(future: Future[void]) =
   if future.cb != nil:
     future.cb()
 
+proc complete*[T](future: FutureVar[T]) =
+  ## Completes a ``FutureVar``.
+  template fut: expr = Future[T](future)
+  checkFinished(fut)
+  assert(fut.error == nil)
+  fut.finished = true
+  if fut.cb != nil:
+    fut.cb()
+
 proc fail*[T](future: Future[T], error: ref Exception) =
   ## Completes ``future`` with ``error``.
   #assert(not future.finished, "Future already finished, cannot finish twice.")
@@ -264,6 +288,13 @@ proc readError*[T](future: Future[T]): ref Exception =
   else:
     raise newException(ValueError, "No error in future.")
 
+proc mget*[T](future: FutureVar[T]): var T =
+  ## Returns a mutable value stored in ``future``.
+  ##
+  ## Unlike ``read``, this function will not raise an exception if the
+  ## Future has not been finished.
+  result = Future[T](future).value
+
 proc finished*[T](future: Future[T]): bool =
   ## Determines whether ``future`` has completed.
   ##