first steps of making 'opt' a first class type for Nim

lib/system/assign.nim

@@ -89,6 +89,19 @@ proc genericAssignAux(dest, src: pointer, mt: PNimType, shallow: bool) =
                        cast[pointer](s +% i*% mt.base.size), mt.base, shallow)
   of tyRef:
     unsureAsgnRef(cast[PPointer](dest), cast[PPointer](s)[])
+  of tyOptAsRef:
+    let s2 = cast[PPointer](src)[]
+    let d = cast[PPointer](dest)
+    if s2 == nil:
+      unsureAsgnRef(d, s2)
+    else:
+      when declared(usrToCell):
+        let realType = usrToCell(s2).typ
+      else:
+        let realType = if mt.base.kind == tyObject: cast[ptr PNimType](s2)[]
+                       else: mt.base
+      var z = newObj(realType, realType.base.size)
+      genericAssignAux(d, addr z, mt.base, shallow)
   else:
     copyMem(dest, src, mt.size) # copy raw bits
 
@@ -115,6 +128,7 @@ when false:
     of tyPtr: k = "ptr"
     of tyRef: k = "ref"
     of tyVar: k = "var"
+    of tyOptAsRef: k = "optref"
     of tySequence: k = "seq"
     of tyProc: k = "proc"
     of tyPointer: k = "range"
@@ -195,7 +209,7 @@ proc genericReset(dest: pointer, mt: PNimType) =
   var d = cast[ByteAddress](dest)
   sysAssert(mt != nil, "genericReset 2")
   case mt.kind
-  of tyString, tyRef, tySequence:
+  of tyString, tyRef, tyOptAsRef, tySequence:
     unsureAsgnRef(cast[PPointer](dest), nil)
   of tyTuple:
     genericResetAux(dest, mt.node)