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Re: Issue: LOAD-OBJECTS (Version 2)
- To: David N Gray <Gray@DSG.csc.ti.com>
- Subject: Re: Issue: LOAD-OBJECTS (Version 2)
- From: David A. Moon <Moon@STONY-BROOK.SCRC.Symbolics.COM>
- Date: Thu, 9 Mar 89 15:58 EST
- Cc: Common-Lisp-Object-System@SAIL.STANFORD.EDU, CL-Compiler@SAIL.STANFORD.EDU
- In-reply-to: <2809731258-5200907@Kelvin>
Date: Fri, 13 Jan 89 18:54:18 CST
From: David N Gray <Gray@DSG.csc.ti.com>
This looks good. The only thing I have doubts about is:
> The function MAKE-LOAD-FORM-USING-SLOTS can be useful in user-written
> MAKE-LOAD-FORM methods. Its first argument is the object. Its
> optional second argument is a list of the names of the slots to
> preserve; it defaults to all of the local slots.
> MAKE-LOAD-FORM-USING-SLOTS returns forms that construct an equivalent
> object using MAKE-INSTANCE and SETF of SLOT-VALUE for slots with
> values, or SLOT-MAKUNBOUND for slots without values, or using other
> functions of equivalent effect.
Rather than having the second argument default to a list of all instance
slots, it might be better to consider two separate cases:
1. If a second argument is supplied, then MAKE-INSTANCE will be used to
create the object, (using INITIALIZE-INSTANCE to default the slot
values), and then the designated slots will be forced to
have the proper value.
2. Without a second argument, ALLOCATE-INSTANCE will be used to create
the object (without invoking INITIALIZE-INSTANCE or
SHARED-INITIALIZE), and then all the slots will be filled in.
If you are going to specify all of the slot values, then there shouldn't
be a need to compute default values, and it may be undesirable to invoke
INITIALIZE-INSTANCE -- for example, it might complain about missing
required arguments or perform undesired side-effects.
I don't think it's a good idea to have such a large deviation in behavior
based on whether an optional argument is present or not. What if the
argument is present but its value is a list of all the slots?
I personally cannot figure out whether calling INITIALIZE-INSTANCE when
it's not wanted, or failing to call it when it is wanted, would cause
more unexpected behavior. I have to resolve that by keeping it simple
so the programmer can figure it out on his own. So I think it should
always create the object with MAKE-INSTANCE.
> The default MAKE-LOAD-FORM method for STANDARD-OBJECT signals an
Wouldn't it be permissible to just not have a default method, so that a
"no applicable method" error is signalled?