fixes #117

compiler/sem.nim

@@ -72,6 +72,10 @@ proc commonType*(x, y: PType): PType =
   elif b.kind in {tyExpr, tyNil}: result = x
   elif a.kind == tyStmt: result = a
   elif b.kind == tyStmt: result = b
+  elif a.kind == tyTypeDesc:
+    # turn any concrete typedesc into the abstract typedesc type
+    if a.sons == nil: result = a
+    else: result = newType(tyTypeDesc, a.owner)
   elif b.kind in {tyArray, tyArrayConstr, tySet, tySequence} and 
       a.kind == b.kind:
     # check for seq[empty] vs. seq[int]

compiler/semexprs.nim

@@ -402,10 +402,10 @@ proc semArrayConstr(c: PContext, n: PNode, flags: TExprFlags): PNode =
       indexType = idx.typ
       x = x.sons[1]
     
-    addSon(result, semExprWithType(c, x))
+    let yy = semExprWithType(c, x)
-    var typ = skipTypes(result.sons[0].typ, {tyGenericInst, tyVar, tyOrdinal})
+    var typ = yy.typ
-    # turn any concrete typedesc into the absract typedesc type
+    addSon(result, yy)
-    if typ.kind == tyTypeDesc: typ.sons = nil
+    #var typ = skipTypes(result.sons[0].typ, {tyGenericInst, tyVar, tyOrdinal})
     for i in countup(1, sonsLen(n) - 1): 
       x = n.sons[i]
       if x.kind == nkExprColonExpr and sonsLen(x) == 2: 
@@ -415,10 +415,15 @@ proc semArrayConstr(c: PContext, n: PNode, flags: TExprFlags): PNode =
           localError(x.info, errInvalidOrderInArrayConstructor)
         x = x.sons[1]
       
-      n.sons[i] = semExprWithType(c, x, flags*{efAllowDestructor})
+      let xx = semExprWithType(c, x, flags*{efAllowDestructor})
-      addSon(result, fitNode(c, typ, n.sons[i]))
+      result.add xx
+      typ = commonType(typ, xx.typ)
+      #n.sons[i] = semExprWithType(c, x, flags*{efAllowDestructor})
+      #addSon(result, fitNode(c, typ, n.sons[i]))
       inc(lastIndex)
     addSonSkipIntLit(result.typ, typ)
+    for i in 0 .. <result.len:
+      result.sons[i] = fitNode(c, typ, result.sons[i])
   result.typ.sons[0] = makeRangeType(c, 0, sonsLen(result) - 1, n.info)
 
 proc fixAbstractType(c: PContext, n: PNode) = 

tests/compile/tcommontype.nim

@@ -0,0 +1,20 @@
+type
+  TAnimal=object {.inheritable.}
+  PAnimal=ref TAnimal
+
+  TDog=object of TAnimal
+  PDog=ref TDog
+
+  TCat=object of TAnimal
+  PCat=ref TCat
+
+  TAnimalArray=array[0..2,PAnimal]
+
+proc newDog():PDog = new(result)
+proc newCat():PCat = new(result)
+proc test(a:openarray[PAnimal])=
+  echo("dummy")
+
+#test(newDog(),newCat()) #does not work
+var myarray:TAnimalArray=[newDog(),newCat(),newDog()] #does not work
+#var myarray2:TAnimalArray=[newDog(),newDog(),newDog()] #does not work either

todo.txt

@@ -7,7 +7,6 @@ version 0.9.2
 - acyclic vs prunable; introduce GC hints
 - CGEN: ``restrict`` pragma + backend support; computed goto support
 - document NimMain and check whether it works for threading
-- make use of commonType relation in expressions
 
 Bugs
 ====