对于一个新项目,我正在考虑使用Fortran2003的面向对象功能。我尝试过的一件事涉及到一个过程指针,它指向一个函数(而不是子程序),该函数返回一个多态类型的指针。我想知道这样的构造是否合法,因为我从不同的编译器那里得到了混合的结果(见下文)。
作为一个具体的例子,考虑以下功能接口:
abstract interface
function if_new_test(lbls) result(t)
import :: test_t
class(test_t),pointer :: t
character(len=*),intent(in) :: lbls(:)
end function if_new_test
end interface
使用代码应该有一个过程指针,可以指向具有以下接口的函数:
procedure(if_new_test),pointer :: nt
我想问这是否合法,因为gfortran(4.7.2)抱怨这个过程的指针声明带有消息:
错误:(1)处的CLASS变量'nt'必须是伪变量、可分配变量或指针
我不理解这个错误消息,因为nt
本身就是一个指针,它指向的函数返回的也是一个指针。
以下是示例的完整源代码,以供参考。第一,包含我的派生类型、接口和函数/子程序的模块:
module test_m
implicit none
type :: test_t
character(len=10) :: label
contains
procedure :: print => print_test
end type test_t
type,extends(test_t) :: test2_t
character(len=10) :: label2
contains
procedure :: print => print_test2
end type test2_t
abstract interface
function if_new_test(lbls) result(t)
import :: test_t
class(test_t),pointer :: t
character(len=*),intent(in) :: lbls(:)
end function if_new_test
subroutine if_make_test(t,lbls)
import :: test_t
class(test_t),pointer :: t
character(len=*),intent(in) :: lbls(:)
end subroutine if_make_test
end interface
contains
subroutine print_test(self)
implicit none
class(test_t),intent(in) :: self
print *, self%label
end subroutine print_test
subroutine print_test2(self)
implicit none
class(test2_t),intent(in) :: self
print *, self%label, self%label2
end subroutine print_test2
function new_test(lbls) result(t)
implicit none
class(test_t),pointer :: t
character(len=*),intent(in) :: lbls(:)
call make_test(t,lbls)
end function new_test
function new_test2(lbls) result(t)
implicit none
class(test_t),pointer :: t
character(len=*),intent(in) :: lbls(:)
call make_test2(t,lbls)
end function new_test2
subroutine make_test(t,lbls)
implicit none
class(test_t),pointer :: t
character(len=*),intent(in) :: lbls(:)
allocate(test_t::t)
t%label = lbls(1)
end subroutine make_test
subroutine make_test2(t,lbls)
implicit none
class(test_t),pointer :: t
character(len=*),intent(in) :: lbls(:)
allocate(test2_t::t)
select type(t) ! so the compiler knows the actual type
type is(test2_t)
t%label = lbls(1)
t%label2 = lbls(2)
class default
stop 1
end select
end subroutine make_test2
end module test_m
而使用该模块的主要程序:
program test
use test_m
implicit none
class(test_t),pointer :: p
procedure(if_make_test),pointer :: mt
procedure(if_new_test),pointer :: nt
mt => make_test
call mt(p,["foo"])
call p%print
deallocate(p)
mt => make_test2
call mt(p,["bar","baz"])
call p%print
deallocate(p)
p => new_test(["foo"])
call p%print
deallocate(p)
p => new_test2(["bar","baz"])
call p%print
deallocate(p)
nt => new_test
p => nt(["foo"])
call p%print
deallocate(p)
nt => new_test2
p => nt(["bar","baz"])
call p%print
deallocate(p)
end program test
该程序首先通过子例程make_test
和make_test2
创建对象,在我的测试中,这适用于我尝试过的所有编译器。接下来,通过直接调用函数new_test
和new_test2
来创建对象,这也适用于我的测试。最后,对象应该再次通过这些函数创建,但要通过过程指针nt
间接创建。
如上所述,gfortran(4.7.2)没有编译nt
的声明。
ifort(12.0.4.191)在nt => new_test
行产生内部编译器错误。
pgfortran(12.9)在没有警告的情况下编译,可执行文件会产生预期的结果。
那么,根据Fortran2003,我试图做的是非法的,还是编译器对这些功能的支持仍然不足?我应该只使用子例程而不是函数吗(因为这似乎很有效)?
您的代码似乎很好。我可以用英特尔13.0.1和NAG 5.3.1编译它,没有任何问题。较老的编译器可能会遇到Fortran 2003中更"花哨"的功能问题。
根据问题的不同,您也可以使用可分配类型而不是指针。另一方面,应该更防内存泄漏,您将无法返回函数的多态类型:
module test_m
implicit none
type :: test_t
character(len=10) :: label
contains
procedure :: print => print_test
end type test_t
type,extends(test_t) :: test2_t
character(len=10) :: label2
contains
procedure :: print => print_test2
end type test2_t
abstract interface
function if_new_test(lbls) result(t)
import :: test_t
class(test_t), allocatable :: t
character(len=*),intent(in) :: lbls(:)
end function if_new_test
subroutine if_make_test(t,lbls)
import :: test_t
class(test_t), allocatable :: t
character(len=*),intent(in) :: lbls(:)
end subroutine if_make_test
end interface
contains
subroutine print_test(self)
class(test_t), intent(in) :: self
print *, self%label
end subroutine print_test
subroutine print_test2(self)
class(test2_t), intent(in) :: self
print *, self%label, self%label2
end subroutine print_test2
subroutine make_test(t,lbls)
class(test_t), allocatable :: t
character(len=*),intent(in) :: lbls(:)
allocate(test_t::t)
t%label = lbls(1)
end subroutine make_test
subroutine make_test2(t,lbls)
class(test_t), allocatable :: t
character(len=*),intent(in) :: lbls(:)
allocate(test2_t::t)
select type(t) ! so the compiler knows the actual type
type is(test2_t)
t%label = lbls(1)
t%label2 = lbls(2)
class default
stop 1
end select
end subroutine make_test2
end module test_m
program test
use test_m
implicit none
class(test_t), allocatable :: p
procedure(if_make_test), pointer :: mt
mt => make_test
call mt(p, ["foo"])
call p%print
deallocate(p)
mt => make_test2
call mt(p, ["bar","baz"])
call p%print
deallocate(p)
end program test
还有一句话:模块级的隐式none语句是由模块过程"继承"的,因此不必在每个额外的子例程中都发出它。