键入构造函数

通过使用接口重载类型名称，可以为派生类型创建自定义构造函数。这样，在构造该类型的对象时，可以使用与组件不对应的关键字参数。

module ball_mod
  implicit none

  ! only export the derived type, and not any of the
  ! constructors themselves
  private
  public::ball

  type::ball_t
     real::mass
  end type ball_t

  ! Writing an interface overloading 'ball_t' allows us to
  ! overload the type constructor
  interface ball_t
     procedure::new_ball
  end interface ball_t

contains

  type(ball_t) function new_ball(heavy)
    logical, intent(in) :: heavy

    if (heavy) then
       new_ball%mass = 100
    else
       new_ball%mass = 1
    end if
    
  end function new_ball
  
end module ball_mod

program test
  use ball_mod
  implicit none

  type(ball_t) :: football
  type(ball_t) :: boulder
  
  ! sets football%mass to 4.5
  football = ball_t(4.5)
  ! calls 'ball_mod::new_ball'
  boulder = ball_t(heavy=.true.)
end program test

与使用单独的初始化例程相比，这可用于制作更整洁的 API：

subroutine make_heavy_ball(ball)
  type(ball_t), intent(inout) :: ball
  ball%mass = 100
end subroutine make_heavy_ball

...

call make_heavy_ball(boulder)