CODEWITHSUNDEEP
arraysfortranpolymorphism
Sam Harrison
Sam Harrison

Reputation: 123

Using assumed-rank Fortran array as derived type component

I'm looking for some general advice as to the best approach to creating a derived type that stores arbitrary data with arbitrary rank.

Say I have a derived type Result with a data component (amongst others):

type, public :: Result
    private
    class(*), allocatable :: data
    ...
end type

which is initialised by some procedure (called from an interface Result):

function init(data) result(this)
  type(Result) :: this
  class(*), intent(in) :: data

  allocate(this%data, source=data)
end function

This works fine for scalar data, but I'm unsure about how to go about setting it up for arbitrary-rank data. I know procedures can accept assumed-rank parameters, so data in the init(data) function could be data(..), but I'm not sure it's possible to specify the derived type property this%data as being a assumed rank?

The other way I thought of doing it would be to store the arbitrary rank data as a scalar, if such a thing is possible in Fortran? This would be equivalent to using the serialize() and unserialize() functions in PHP. If anyone has any guidance on a similar approach, I'd be very grateful.

Ultimately I'd like to be able to do something like this:

type(Result) :: scalarResult
type(Result) :: 2DResult

scalarResult = Result(data=1.234)
2DResult = Result(data=[[1,2,3],[4,5,6]])

Upvotes: 3

Views: 504

Answers (1)

Steve Lionel
Steve Lionel

Reputation: 7267

It's not possible to have an assumed rank derived type component. You'll need to find another solution, such as what Vladimir suggests. Another idea, which is sort of a kluge, is to store the C_LOC of the data and the rank, call out to a C routine that constructs an appropriate C descriptor and then calls back in to a Fortran routine with an assumed-rank argument.

Do keep in mind that you can't do a lot with assumed rank in Fortran - SELECT RANK doesn't exist until F2015.

Upvotes: 2

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