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Re: Suggestion - rlet with clear
- To: email@example.com (Jeffrey B Kane)
- Subject: Re: Suggestion - rlet with clear
- From: firstname.lastname@example.org (Bill St. Clair)
- Date: Mon, 8 Feb 1993 14:48:29 -0600
- Cc: info-mcl
>I wanted to throw out a suggestion for an optional argument to
>the rlet macro which first clears any structures it allocates
>with NewPtr (and before it makes any assignments to the fields).
>I have several cases where I have to manually clear the fields.
>I would try using the ccl::%clear-pointer or ccl::%clear-block but
>there are two problems:
>1) They are undocumented
>2) I then have to add a statemtent to assign each field and lose the
> convenience of the rlet macro.
>An example might be:
>(rlet ((p :ParamBlockRec :clear t
> :ioNamePtr volName
> :ioVRefNum vRefNum))
> (#_SomeHFSCall pb)
> (pref pb :ParamBlockRec.ioResult))
MCL already has a feature similar to what you're asking for. It is
undocumented, but I will add it to my list of things that need to
be exported and documented for MCL 2.1. The macro is called
CCL::RLETZ. Its syntax is identical to RLET. The difference is
that it expands into a %STACK-BLOCK form with (... :CLEAR t) specified
for each variable (this is an undocumented feature of %STACK-BLOCK).
The %STACK-BLOCK form compiles into a call to a kernel function that
does the clearing in a tight assembly language loop.
'(ccl::rletz ((pb :ParamBlockRec
(pref pb :ParamBlockRec.ioResult))))
(%STACK-BLOCK ((PB 80 :CLEAR T))
(SETF (%GET-PTR PB 18) VOLNAME)
(SETF (%GET-SIGNED-WORD PB 22) VREFNUM)
(PREF PB :PARAMBLOCKREC.IORESULT))