replace_one_occurrence Function

   elemental function replace_one_occurrence(self, old, new) result(replaced)
   !< Return a string with the first occurrence of substring old replaced by new.
   !<
   !< @note The doctest is not necessary, this being tested by [[string:replace]].
   class(string),             intent(in)  :: self      !< The string.
   character(kind=CK, len=*), intent(in)  :: old       !< Old substring.
   character(kind=CK, len=*), intent(in)  :: new       !< New substring.
   type(string)                           :: replaced  !< The string with old replaced by new.
   integer                                :: pos       !< Position from which replace old.

   if (allocated(self%raw)) then
      replaced = self
      pos = index(string=self%raw, substring=old)
      if (pos>0) then
         if (pos==1) then
            replaced%raw = new//self%raw(len(old)+1:)
         else
            replaced%raw = self%raw(1:pos-1)//new//self%raw(pos+len(old):)
         endif
      endif
   endif
   endfunction replace_one_occurrence