Fortran 基本函数与基本子例程
Fortan 允许基本子例程具有intent(inout) 和intent(out) 参数，但基本函数仅允许intent(in)。
这是为什么？这只是一种风格约定，还是调用函数和调用子例程之间存在一般性的不同？
换句话说，
Elemental Integer Function FOO(i)
Integer, intent(in) :: i
...
FOO=something
End Function
FOO 的这些实现是否同样
Elemental Subroutine FOO(i, v)
Integer, intent(in) :: i
Integer, intent(out) :: v
...
v=something
End Subroutine
有效？
Fortan allows elemental subroutines to have intent(inout) and intent(out) arguments, but elemental functions are only allowed intent(in).
Why is that? Is it just a stylistic convention, or is there something generically different about invoking functions and calling subroutines?
In other words,
Elemental Integer Function FOO(i)
Integer, intent(in) :: i
...
FOO=something
End Function
and
Elemental Subroutine FOO(i, v)
Integer, intent(in) :: i
Integer, intent(out) :: v
...
v=something
End Subroutine
— are these implementations of FOO equivalently efficient?
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没有至少一个标记为
intent(out)或intent(inout)的参数的基本子例程是没有意义的，因为您必须以某种方式传递结果。函数有其返回值，子例程必须使用其参数。在 Fortran 2008 中，据我所知，基本过程不必是纯粹的，但仅通过其副作用很难想象一个有用的基本子例程。There is no point in having an elemental subroutine without at least one argument marked as
intent(out)orintent(inout), because you have to pass the result somehow. A function has its return value, a subroutine must use its arguments. In Fortran 2008 AFAIK elemental procedures doesn't have to be pure, but it's hard to imagine a useful elemental subroutine only through its side effects.