042. Zero-size array constructor#

[data_type ::] is a zero-size array of type data_type. See examples below.

zero-size.f90 | | ₀ |

program zero_size
   implicit none

   associate ( &
      r0 => [real ::], &
      d0 => [real(kind(1.0d0)) ::], &
      i0 => [integer ::], &
      c20 => [character(len=2) ::], &
      c50 => [character(len=5) ::])

   print *, size(r0), kind(r0)   ! 0 4
   print *, size(d0), kind(d0)   ! 0 8
   print *, size(i0), kind(i0)   ! 0 4
   print *, size(c20), len(c20)  ! 0 2
   print *, size(c50), len(c50)  ! 0 5

   end associate  ! Required
end program zero_size

Output1#

           0           4
           0           8
           0           4
           0           2
           0           5

From the Tweet comments, one potential use for this is that “if a procedure has a required argument that is an integer array, you can pass [integer ::] from the caller.”

Note

The associate construct, used here, “yields simple abbreviations for more complex statements. It can be an alias for expressions or variables.”2

[data_type :: ] is a zero-size array of type data_type.pic.twitter.com/XmBx5W4ZBG
— FortranTip (@fortrantip) December 23, 2021

1: Compiled using GNU Fortran (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0 with no flags
2: https://fortranwiki.org/fortran/show/associate