Editing Variadic function (section)

=== In Fortran ===
Since the Fortran 90 revision, [[Fortran]] functions or subroutines can accept optional arguments:<ref>{{Cite web |title=Optional Arguments |url=https://www.intel.com/content/www/us/en/docs/fortran-compiler/developer-guide-reference/2023-0/optional-arguments.html |access-date=2025-03-18 |website=Intel |language=en}}</ref> the argument list is still fixed, but the ones that have the {{code|optional}} attribute can be omitted in the function/subroutine call. The intrinsic function {{code|present()}} can be used to detect the presence of an optional argument. The optional arguments can appear anywhere in the argument list. 

<syntaxhighlight lang="fortran">program test
implicit none

    real :: x
    
    !> all arguments are passed:
    call foo( 1, 2, 3.0, 4, x )
    !< outputs 1 \ 2 \ 3.0 \ 4 \ 6.0 (the "\" denotes a newline)
    
    !> the last 2 arguments are omitted:
    call foo( 1, 2, 3.0 )
    !< outputs 1 \ 2 \ 3.0
    
    !> the 2nd and 4th arguments are omitted: the arguments that are positioned after 
    !> an omitted argument must be passed with a keyword:
    call foo( 1, c=3.0, e=x ) 
    !< outputs 1 \ 3.0 \ 6.0
    
    !> alternatively, the Fortran 2023 revision has introduced the .NIL. pseudo constant
    !> to denote an omitted argument
    call foo( 1, .NIL., 3.0, .NIL., x )
    !< outputs 1 \ 3.0 \ 6.0

contains

    !> the subroutine foo() has 2 mandatory and 3 optional arguments
    subroutine foo( a, b, c, d, e )
        integer, intent(in)            :: a 
        integer, intent(in),  optional :: b
        real,    intent(in)            :: c
        integer, intent(in),  optional :: d
        real,    intent(out), optional :: e
        
        print*, a
        if (present(b)) print*, b 
        print*, c
        if (present(d)) print*, d
        if (present(e)) then
            e = 2*c
            print*, c
        end if
    end subroutine

end program</syntaxhighlight>

'''Output:'''

<pre>
The sum of [1 2] is 3 
The sum of [1 2 3] is 6 
The sum of [1 2 3 4] is 10
</pre>