Fortran/OOP in Fortran

Fortran Object-oriented programming Module Overview Data can be gathered in modules. The general form is given by module <name> [use <module_names>] [<declarations>] contains [<subroutines and functions>] end module [<name>] Data access There are three possible access properties: public, private, protected. public: Outside code has read and write access. private: Outside code has no access. public, protected: Outside code has read access. Using module in other code One can include the module's public data in outside code. There are three ways. use <moduleName>: includes all public data and methods use <moduleName>, <renames>: includes all public data and methods, but renames some public data or methods use <moduleName>, only: <subset>: includes only some public data and methods Example General overview module test_m implicit none private ! All data is by default private. ! These procedures are set public -> accessible outside public print_coords, set_coords real :: x, y ! Not accessible outside module. contains subroutine print_coords print *, "x, y", x, y end subroutine subroutine set_coords(new_x, new_y) real, intent(in) :: new_x, new_y x = new_x y = new_y end subroutine end module program main use test_m ! Import the "test_m" module implicit none call set_coords(1.0, 1.0) ! Call the public procedure from test_mod call print_coords end program Data access module data_access_m implicit none private public a, b protected b private c integer :: a = 1 integer :: b = 1 integer :: c = 1 end module program main use data_access_m ! Accessing public object works. print *, a ! Editing public object works. a = 2 ! Accessing protected object works. print *, b ! Editing protected object does not work. !b = 2 <- ERROR ! Accessing private object does not work !print *, c <- ERROR ! Editing private object does not work !c = 2 <- ERROR end program Using modules module test_module implicit none private integer, public :: a = 1 integer, public, protected :: b = 1 integer, private :: c = 1 end module test_module !> Import all public data of test_module. program main use test_module print *, a, b end program main !> Import all data, and rename. program main use test_module, better_name => a ! New name use available. print *, better_name ! Old name is not available anymore. !print *, a <- ERROR end program main !> Import only a subset of the public data. program main use test_module, only : a ! Only a is loaded print *, a ! b is not loaded !print *, b <- ERROR end program main Submodule Modules can be extended using submodules. Multiple advantages arise splitting of large modules splitting of interface definitions and implementations such that dependent modules do not need to be recompiled if the implementations change two modules need data from each other. Example Splitting of definitions and implementations !> simple module about circles module circle_mod implicit none private public :: area, radius real :: radius real, parameter :: PI = 3.1415 interface ! Interface block needed. Each function implemented via submodule needs an entry here. module function area() ! Important. Note the "module" keyword. real :: area end function end interface end module submodule (circle_mod) circle_subm ! Submodule (parent_mod) child_mod. contains module function area() ! Again "module" keyword. area = PI*radius**2 end function end submodule program main use circle_mod implicit none radius = 1.0 print *, "area:", area() end program Derived data types In Fortran one can derive structures off of other structures, so called derived data types. The derived types will have the features of the parent type as well as the newly added ones and the general syntax is given by: type, extends(<parentTypeName>) :: <newTypeName> <definitions> end type The following example shows different types of people within a company. module company_data_mod implicit none private public phone_type, address_type, person_type, employee_type, salaried_worker_type, hourly_worker_type type phone_type integer :: area_code, number end type type address_type integer :: number character (len=:), allocatable :: street, city character (len=2) :: state integer :: zip_code end type type person_type character (len=:), allocatable :: name type (address_type) :: address type (phone_type) :: phone character (len=:), allocatable :: remarks end type type, extends (person_type) :: employee_type integer :: phone_extension, mail_stop, id_number end type type, extends (employee_type) :: salaried_worker_type real :: weekly_salary end type type, extends (employee_type) :: hourly_worker_type real :: hourly_wage, overtime_factor, hours_worked end type end module program main use company_data_mod implicit none type (hourly_worker_type) :: obj end program Destructors One can define procedures which will be invoked before the object is automatically deleted (out of scope). This is done with the statement final. The following example illustrates it module person_m implicit none type person integer, allocatable :: numbers(:) contains final :: del end type contains subroutine del(this) !! example for a derived type's destructor. allocatables are !! deallocated automatically anyways. this is just to show the usage of !! "final". type (person), intent (inout) :: this if (allocated(this%numbers)) deallocate (this%numbers) end subroutine end module Abstract base type and deferred procedure One can set the base type as abstract such that one cannot initialize objects of that type but one can derive sub-types of it (via extends). Specific procedures which should be defined in the sub-type need the property deferred as well as an explicit interface. The following example illustrates their use. module shape_m implicit none type, abstract :: shape real :: a, b contains procedure :: print => shape_print procedure (area_shape), deferred :: area end type interface real function area_shape(this) import :: shape class (shape), intent (in) :: this end function end interface contains subroutine shape_print(this) class (shape), intent (in) :: this print *, 'a,b', this%a, this%b end subroutine end module module line_m use shape_m implicit none private public line type, extends (shape) :: line contains procedure :: area end type contains real function area(this) class (line), intent (in) :: this area = abs(this%a - this%b) end function end module module rectangle_m use shape_m implicit none private public rectangle type, extends(shape) :: rectangle contains procedure :: area end type contains real function area(this) class (rectangle), intent (in) :: this area = this%a * this%b end function end module program main use line_m use rectangle_m implicit none type (line) :: l type (rectangle) :: r ! line l%a = 2.0 l%b = 4.0 print *, "line ... " call l%print print *, "-> from: ", l%a print *, "-> to: ", l%b print *, "-> length:", l%area() ! rectangle r%a = 3.0 r%b = 5.0 print * print *, "rectangle ..." call r%print print *, "-> side a:", r%a print *, "-> side b:", r%b print *, "-> area: ", r%area() end program Polymorphic Pointer One can create pointers to child classes by using type definitions in allocate statements and the select type environment. The following example highlights its use. module shape_m implicit none type, abstract :: shape ! Just an empty class used to implement a parent class. ! reason for abstract: there shouldnt be objects of TYPE(!) shape, just ! polymorphic CLASS instances. end type end module module line_m use shape_m implicit none type, extends (shape) :: line ! A child class w/ one attribute. ! Reason for extends(shape): polymorphic shape pointer can point to ! objects of this type. real :: length end type end module module rectangle_m use shape_m implicit none type, extends (shape) :: rectangle ! A child class w/ another attribute ! Reason for extends(shape): (see explanation in line type) real :: area end type end module program main use rectangle_m use line_m implicit none class (shape), allocatable :: sh ! Pointer to parent class. ! allocate (line :: sh) allocate (rectangle :: sh) ! Allocate using child types select type (x => sh) ! Associate block. "x" will be a pointer to the child object and of its type(!!) type is (line) ! Select the right child type (the one we used in the allocate statement) x%length = 1.0 print *, 'line length', x%length type is (rectangle) x%area = 2.0 print *, 'rectangle area', x%area ! class is () ! Select by using classes. class default ! If nothing of the above applied. error stop 'class/type not specified!' end select end program