with Ada.Strings.Fixed;
with Ada.Text_IO;

procedure StringInsertSpaces is
  s : String(1..10) := (others => ' ');
begin
  s(1) := 'a';
  s(2) := 'b';
  for i in 1 .. s'length + 5 loop
    Ada.Text_IO.Put_Line(""""&s&"""");
    Ada.Strings.Fixed.Insert(s, 2, "x");
  end loop;
end StringInsertSpaces;

-- Output:
-- "ab        "
-- "axb       "
-- "axxb      "
-- "axxxb     "
-- "axxxxb    "
-- "axxxxxb   "
-- "axxxxxxb  "
-- "axxxxxxxb "
-- "axxxxxxxxb"
--
-- raised ADA.STRINGS.LENGTH_ERROR : a-strfix.adb:360
--
-- Ie, Ada.Strings.Fixed.Insert treats spaces differently
-- than all other characters.  It will happily throw away
-- spaces that fall off the end of the string, but it will
-- raise an exception when any other kind of character would
-- be similarly discarded.
--
-- See also StringInsert