回调函数
回调函数是作为参数传递给另一个函数的函数。 创建此类回调函数的首选方法是提供抽象接口(abstract interface)声明回调函数的特征。 这样可以对传递的回调函数进行编译时检查。
module integrals
use types, only: dp
implicit none
private
public :: simpson, integrable_function
abstract interface
function integrable_function(x) result(func)
import :: dp
real(dp), intent(in) :: x
real(dp) :: func
end function integrable_function
end interface
contains
function simpson(f, a, b) result(s)
real(dp), intent(in) :: a, b
procedure(integrable_function) :: f
real(dp) :: s
s = (b-a) / 6 * (f(a) + 4*f((a+b)/2) + f(b))
end function simpson
end module integrals
然后,通过导入模块,该函数将作为回调函数使用,如下例所示,
module demo_functions
use types, only: dp
implicit none
private
public :: test_integral
contains
subroutine test_integral(a, k)
real(dp), intent(in) :: a, k
print *, simpson(f, 0._dp, pi)
print *, simpson(f, 0._dp, 2*pi)
contains
function f(x) result(y)
real(dp), intent(in) :: x
real(dp) :: y
y = a*sin(k*x)
end function f
end subroutine test_integral
end module demo_functions
如果导出抽象接口,可以创建具有正确特征的过程指针, 还可以进一步扩展回调函数,如下所示,
module demo_integrals
use types, only: dp
use integrals, only: simpson, integrable_function
implicit none
private
public :: simpson2, integrable_function
contains
function simpson2(f, a, b) result(s)
real(dp), intent(in) :: a, b
procedure(integrable_function) :: f
real(dp) :: s
real(dp) :: mid
mid = (a + b)/2
s = simpson(f, a, mid) + simpson(f, mid, b)
end function simpson2
end module demo_integrals