On 11 Jun 2011, at 10:42, Nick Levine wrote:
> Actually, looking through my code base, I find I've used &aux half a
> dozen times in the last ten years. Always in a BOA constructor.
I have a tendency to use &aux more and more often, even outside of BOA
constructors. There are two main reasons:
- It saves horizontal space in the source code. Compare the following two
pieces of code:
(defun foo1 (a b c &aux d e f)
...)
(defun foo2 (a b c)
(let (d e f)
...))
The use of &aux saves one level of indentation here, which can sometimes make a
piece of code look more beautiful.
- The more important reason is that I sometimes want to derive some value from
an argument that is "very close" to the value of the original argument. Here is
an example:
(defun required-args (args)
(loop for arg in args until (member arg lambda-list-keywords) collect arg))
(defun process-method-arguments (args &aux (required-args (required-args args)))
...)
This is, of course, only a subjective quality, but in cases like this, the
function actually only wants to do something with the required arguments for a
method definition, but it also wants the client code not to worry too much
about what it passes to the function. To me, &aux perfectly expresses that idea.
Best,
Pascal
--
Pascal Costanza
The views expressed in this email are my own, and not those of my employer.
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