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From: Dick Hendrickson <dick.hendrickson@att.net>
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Subject: Re: another way to shoot yourself in the foot?
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Date: 2008-07-10T20:45:03+00:00
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James Giles wrote:
> Craig Powers wrote:
>> Dick Hendrickson wrote:
>>> Colin Paul Gloster wrote:
>>>> Does Fortran always automatically check if the INTERFACE actually
>>>> corresponds to the code?
>>>>
>>> Depends on the compiler, but in general NO.  I think all
>>> compilers will detect an explicit assignment to a dummy
>>> argument that has INTENT(IN) in the subroutine; I'm not sure
>>> any will detect an assignment if the dummy is passed on
>>> to another routine and that routine (illegally) assigns to
>>> its argument.
>> Is that actually possible without lying about an interface?  i.e. Is
>> it possible to pass an INTENT(IN) dummy as an actual argument to a
>> more permissive dummy argument in another routine (no intent or
>> intent OUT)
> 
> It's not permitted.  The standard doesn't require implementations to
> verify that it's not done.  That is, it's not one of the kinds of error
> that the standard requires implementations to detect and report.
> 
You're partially wrong, James.  It is permitted to pass a dummy
with INTENT(IN) to a subroutine that doesn't specify either
INTENT(INOUT) or INTENT(OUT).  You can pass them to a subroutine
that doesn't specify intent and even potentially modifies
its argument.  You can't lie in an interface, but you can
call routines that don't have an interface.  Those routines are
required to do the right thing; but the compiler isn't required
to detect violations.

Dick Hendrickson