Provides an abstract container derived type which can be used as a sort of unlimited polymorphic entity whose contents are retrievable with type-guards. Different subclasses are created in order to hold different data-types. Subclasses are provided for the default variable types in Fortran. The abstract type can be used within data structures to so that a single implementation can hold arbitrary types of contents. The type of the contents can be selected when the data structure is constructed, by passing a particular subclass of the abstract container to the constructor.

At present the single greatest weakness of this project is that it does not support the storage of arrays--only scalars (although scalar coarrays should be fine). It is unclear whether or not a solution to this problem is readily available.

Extensions to the abstract type must implement the procedure typeguard, which tests that variables being passed to the container or to which the container's contents are assigned are of the correct type. An example of a concrete implementation to hold a user-defined derived type is provided below.

module example_container_mod

  use abstract_container_mod
  implicit none
  private

  type example
    integer, public :: i
  end type example

  type, extends(container_type) :: example_container
  contains
    private
    procedure :: typeguard => example_guard
  end type example_container

contains

  logical function example_guard(this, lhs) result(ret)
    class(example_container), intent(in) :: this
    class(*), intent(inout) :: lhs
    select type(lhs)
      type is(example)
        lhs = transfer(this%contents(), lhs)
        ret = .true.
      class default
        ret = .false.
    end select
  end function example_guard

end module example_container_mod

PolyCon is known to work with Gfortran 5.3.0 and ifort 16.0.1 on Ubuntu/Linux Mint. It is known not to work for storing character strings when using Gfortran 4.8. The latter requires the -assume realloc_lhs to be used. A makefile is provided which calls gfortran-5. Static and shared libraries are compiled using make static and make shared, respectively. The test program can be build using make test. At present there is no facility to install the libraries on your system.

PolyCon can be used to create generic data structures. An example implementation of a stack data structure (as well as a test program) can be found in src/test/stack.f90. This can be compiled with make stack.

In addition to the documentation in the README, the API is documented using FORD. This documentation can be found in the ./doc directory in the repository.

This code is licensed under the GPLv3. More permissive licensing may be considered in future.