On Mon, 19 Feb 2018 20:14:29 +0000, Jesse 1 Robinson wrote:

>I can't speak for BPXWDYN, but I remember when REUSE became available in TSO. 
>Before that, a CLIST writer (this was before REXX was ported to TSO) had to 
>code like this:
>FREE DD(like-I-care-if-it's-allocated)
>ALLOC DD(now-I-want-it) ...
>This was necessary because if the DD was not already allocated, a gratuitous 
>FREE would give the user a snarky message to that effect. 
I recall an era when FREE of an unallocated DDNAME was fatal to the CLIST
(of course, the programmer should know better!) but ALLOCATE of a DDNAME
in use merely gave a snarky message.  So, I resorted to:
    ALLOCATE (like-I-care)
    ALLOCATE (now-I-want-it).

RTDDN was a boon.  I still shudder when I see programmers using RANDOM() to
generate DDNAMEs and hoping for the best.

>With REUSE, the allocation would take place with no distraction to the user 
>either way.
For many years, REUSE did not work for UNIX files (it's better now).  I think 
was some semantic confusion about the overloading of "REUSE" and UNIX 
could never be reused (like-I-care).  For some of the interim, BPXWDYN 
generously added an internal FREE when the programmer coded REUSE.

>The result was the *same* DD allocated to the data set(s) desired. This goes 
>back to around 1980 +/-.  
But I believe that the OP wanted the *same* data set allocated to two different
DDNAMES, or at least not to disrupt the existing allocation, and allocation
conversion or the REUSE option thwarts that.

I don't know the meaning or the intent of allocation conversion, except that 
it's a PITA.

-- gil

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