slen Function

   elemental function slen(self) result(l)
   !< Return the length of a string.
   !<
   !<```fortran
   !< type(string) :: astring
   !< astring = 'Hello World!   '
   !< print "(L1)", astring%len()==len('Hello World!   ')
   !<```
   !=> T <<<
   class(string), intent(in) :: self !< The string.
   integer                   :: l    !< String length.

   if (allocated(self%raw)) then
      l = len(string=self%raw)
   else
      l = 0
   endif
   endfunction slen