ptrops: add makeUncheckedArray (#193)

turns a pointer into an array pointer of the same type

stew/ptrops.nim

@@ -49,10 +49,13 @@ template distance*[T](a, b: ptr T): int =
   # exceeds what can be represented in an int
   distance(cast[pointer](a), cast[pointer](b)) div sizeof(T)
 
-proc baseAddr*[T](x: openArray[T]): ptr T =
+func baseAddr*[T](x: openArray[T]): ptr T =
   # Return the address of the zero:th element of x or `nil` if x is empty
   if x.len == 0: nil else: cast[ptr T](x)
 
+func makeUncheckedArray*[T](p: ptr T): ptr UncheckedArray[T] =
+  cast[ptr UncheckedArray[T]](p)
+
 template makeOpenArray*[T](p: ptr T, len: Natural): openArray[T] =
   toOpenArray(cast[ptr UncheckedArray[T]](p), 0, len - 1)
 

tests/test_ptrops.nim

@@ -86,3 +86,8 @@ suite "ptrops":
       check:
         baseAddr(makeOpenArray(nil, int, 0)) == nil
         baseAddr(makeOpenArray(addr v, 1)) == addr v
+
+    block ua:
+      var v = [2, 3]
+      check:
+        makeUncheckedArray(baseAddr v)[1] == 3