Ondřej,
You've got a long section section on callbacks and the associated
'type casting'. It's useful to see, in order to contrast and compare,
the different ways it _could_ be done, but you've left out what is
arguably the 'best' way to do this in modern Fortran.
To adapt your example of an integration method, this would look
something like this.
module integrals
use types, only: dp
implicit none
private
public :: integrand, simpson
! User extends this type
type, abstract :: integrand
contains
procedure(func), deferred :: eval
end type
abstract interface
function func(this, x) result(fx)
import :: integrand, dp
class(integrand) :: this
real(dp), intent(in) :: x
real(dp) :: fx
end function
end interface
contains
real(dp) function simpson(f, a, b) result(s)
class(integrand) :: f
real(dp), intent(in) :: a, b
s = ((b-a)/6) * (f%eval(a) + 4*f%eval((a+b)/2) + f%eval(b))
end function
end module
The abstract type prescribes exactly what the integration routine
needs, namely a method to evaluate the function, but imposes nothing
else on the user. The user extends this type, providing a concrete
implementation of the eval type bound procedure and adding necessary
context data as components of the extended type.
Here's your usage example adapted to this better method:
module example_usage
use types, only: dp
use integrals, only: integrand, simpson
implicit none
private
public :: foo
type, extends(integrand) :: my_integrand
real(dp) :: a, k
contains
procedure :: eval => f
end type
contains
function f(this, x) result(fx)
class(my_integrand) :: this
real(dp), intent(in) :: x
real(dp) :: fx
fx = this%a*sin(this%k*x)
end function
subroutine foo(a, k)
real(dp) :: a, k
type(my_integrand) :: my_f
my_f%a = a
my_f%k = k
print *, simpson(my_f, 0.0_dp, 1.0_dp)
print *, simpson(my_f, 0.0_dp, 2.0_dp)
end subroutine
end module
A second general comment about the website. It would appear to present
itself as a consensus view of the Fortran community (especially given
the domain name.) Until that time it actually does, I'd suggest making
it clear that you are the author and that the content really reflects
your views on the topic. Nevertheless, I think that websites like this
would be immensely useful to the community, and I applaud you for your
effort.
Best regards,
Neil
On Mon, 2012-06-04 at 23:08 -0700, Ondřej Čertík wrote:
> Hi,
>
> I wanted to publicly announce a modern Fortran webpage that I have
> been working on for some time:
>
> http://fortran90.org/
