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From: Craig Powers <craig.powers@invalid.invalid>
Newsgroups: comp.lang.ada,comp.lang.fortran
Subject: Re: another way to shoot yourself in the foot?
Date: Thu, 10 Jul 2008 16:45:48 -0400
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Date: 2008-07-10T16:45:48-04:00
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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.

Actually, that's not exactly right.  It's not permitted to pass an 
INTENT(IN) to a dummy with intent OUT (i.e. INTENT(INOUT) or 
INTENT(OUT)), this is a constraint in 5.1.2.3 in the F95 draft as well 
as constraint C545 in the F03 draft, so I think it would require a 
diagnostic.

However, it IS permitted to pass an INTENT(IN) to an unspecified INTENT 
dummy, and in that case it would be possible to modify it (and I 
wouldn't expect a compiler to even realistically be able to detect that 
except in very specific circumstances).