Why is the type not accessible?

问题:

I'm trying to return a type from a fortran function. This is the code.

module somemodule
implicit none
! define a simple type
type sometype
   integer :: someint
end type sometype
! define an interface 
interface
   ! define a function that returns the previously defined type
   type(sometype) function somefunction()
   end function somefunction
end interface
contains
end module somemodule

In gfortran (4.4 & 4.5) I get the following error:

Error: The type for function 'somefunction' at (1) is not accessible

I compiled the file as:

gfortran -c ./test.F90

I tried to make the type explicitly public but that didn't help. I was planning to use a c version of the somefunction, that is why I put it in the interface section.

Why is the type not accessible?

回答1:

Adding import inside the function definition fixes this. Due to what many consider a mistake in the design of the language, definitions aren't inherited inside of an interface. The "import" overrides this to achieve the sensible behavior.

interface
   ! define a function that returns the previously defined type
   type(sometype) function somefunction()
   import
   end function somefunction
end interface

回答2:

The answer to the question why it is not accessible is that the standard committee designed it like that. The interface has a separate scope from the enclosing module, so you have to explicitly import names from it. Obviously(?) you can't use the module inside itself, so the import statement is needed.