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From: matthias@mpx1.lanl.gov (Bjorn E. Matthias, M/S H831, 7-6241 or 7-7906)
Newsgroups: comp.lang.fortran
Subject: Re: Type punning in FORTRAN (was in C)
Message-ID: <1131@mpx1.lanl.gov>
Date: 15 Oct 89 19:18:41 GMT
References: <475@idacrd.UUCP> <1989Oct10.185851.6490@agate.berkeley.edu> <1989Oct11.091619.18336@gdt.bath.ac.uk> <1654@l.cc.purdue.edu> <1989Oct13.090311.9760@gdt.bath.ac.uk> <1874@sunset.MATH.UCLA.EDU>
Organization: LAMPF Data Analysis Center, Los Alamos NM
Lines: 38

In article <1874@sunset.MATH.UCLA.EDU>, pmontgom@sonia.math.ucla.edu (Peter Montgomery) writes:
> In article <1989Oct13.090311.9760@gdt.bath.ac.uk> exspes@gdr.bath.ac.uk 
> (P E Smee) writes:
>>
>>The need for a construct to permit type punning is clear, particularly
>>if you're doing 'systemmy' work.  
>>
>>This provides an explicit instruction to the compiler, and (more
>>importantly) a warning to future maintainers of the code, that you are
>>about to willfully, knowledgeably, and intentionally, cheat the data
>>typing and conversion rules.  Every serious language should have such a
>>thing.  (Unfortunately, it seems that most don't, sigh...)
>>
> 	If I read the June, 1989 draft F8X correctly, then the
> new TRANSFER intrinsic function (p. 13-51, section 13.13.108)
> will do precisely this.  The syntax is
> 
> 	result = TRANSFER(SOURCE, MOLD, SIZE) .
> 
> It "returns a result with a physical representation identical to that
> of SOURCE but interpreted with the type and type parameters of MOLD."
> The last argument, SIZE, is optional and affects the array shape
> of the result when SOURCE and MOLD have different sizes
> (e.g., double precision and character).
> 

If I am not mistaken, then this could be previously accomplished in
VAX FORTRAN with EQUIVALENCE between two variables of whatever types.
I have used this often and it appears that TRANSFER is different only
in that one truly has *two* pieces of data, two memory locations.
Sounds like a useful function, though I do not believe it really
introduces a "new" feature.
Forgive me if I am stating what is obvious to all others.
Regards,

Bjorn Matthias

BITNET : MATTHIAS@LAMPF