fixes #1188

lib/pure/concurrency/threadpool.nim

@@ -251,7 +251,10 @@ proc `^`*[T](fv: FlowVar[ref T]): ref T =
   ## Blocks until the value is available and then returns this value.
   blockUntil(fv)
   let src = cast[ref T](fv.data)
-  deepCopy result, src
+  when defined(nimV2):
+    result = src
+  else:
+    deepCopy result, src
   finished(fv)
 
 proc `^`*[T](fv: FlowVar[T]): T =
@@ -259,7 +262,10 @@ proc `^`*[T](fv: FlowVar[T]): T =
   blockUntil(fv)
   when T is string or T is seq:
     let src = cast[T](fv.data)
-    deepCopy result, src
+    when defined(nimV2):
+      result = src
+    else:
+      deepCopy result, src
   else:
     result = fv.blob
   finished(fv)

lib/system/threads.nim

@@ -136,9 +136,12 @@ else:
       when TArg is void:
         thrd.dataFn()
       else:
-        var x: TArg
-        deepCopy(x, thrd.data)
-        thrd.dataFn(x)
+        when defined(nimV2):
+          thrd.dataFn(thrd.data)
+        else:
+          var x: TArg
+          deepCopy(x, thrd.data)
+          thrd.dataFn(x)
     finally:
       afterThreadRuns()