+ import std.math;
  import std.typecons;
- import std.math;
  /*
   Out of array of strings, return the longest one. Return the first one in case of multiple
-     strings of the same length. Return null in case the input array is empty.
? ----

+ strings of the same length. Return null in case the input array is empty.
-     >>> longest([])
? ----

+ >>> longest([])
-     None
+ None
-     >>> longest(["a", "b", "c"])
? ----

+ >>> longest(["a", "b", "c"])
-     "a"
+ "a"
-     >>> longest(["a", "bb", "ccc"])
? ----

+ >>> longest(["a", "bb", "ccc"])
+ "ccc"
-     "ccc"
-     
  */
  Nullable!(string) longest(string[] strings)