var
  left,right,result:Array of Int32;
begin
  left := [1,2,3,4];
  result := left;
  right := [5,6,7];
  Insert(right,result,length(result));

  WriteLn(result); //this works tho, as left is typed as "var Array of Int32"
end.

//.... (this failes)
//> right := [5,6,7];
//> result:= [1,2,3,4] + arr2;

//.... (this works failes)
//> right := [5,6,7];
//> result:= TIntArray([1,2,3,4]) + arr2;

//where TIntArray = Array of Int32;