From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2005-06-30 05:53:14
Greer, Joe wrote:
>>From: David Abrahams <dave_at_[hidden]>
>>>Rob Stewart <stewart_at_[hidden]> writes:
>>>> When classifying types, it is often necessary to test for any
>>>> one of several variations of an aspect. A common case is
>>>> ignoring an aspect which means to allow a match for any
>>>> variation of that aspect
> Please excuse me for jumping into the middle of this discussion. I am
> only a budding metaprogrammer, so that influences how I read things like
> this, so bear with me. With this phrasing,
Being unfamiliar with a topic is a very valuable for a proof-reader (unfortunately
also "fragile" because humans -- and especially those reading this list -- tend to
learn quickly ;-) ).
However, I don't believe this particular case is metaprogramming-specific -- let's
clear up the logic, first:
> it is unclear to me whether
> the common case is "ignoring an aspect" or if it is really "allowing a
> match for any variation of an aspect"
Given a variable 'a' which can be either '1', '2' or '3' it doesn't make a difference:
if ((a == 1) || (a == 2) || (a == 3)) // match any variation of a
// do something
is logically equivalent to
// no if -- just ignore a
// do something
> which I can do by "ignoring an
Equivalence is commutative:
You can ignore 'a' by allowing any variation and you can allow any variation by
ignoring 'a' -- no difference, again.
Making any difference would be talking about implementation details in a parapraph
about plain logic.
>>Neither quoted sentence seems long or complex. Perhaps there
>>was something you snipped to which you were referring?
>>Here's the full text of my suggestion:
>> When classifying types, it is often necessary to test for any
>> one of several variations of an aspect. A common case is
>> ignoring an aspect which means to allow a match for any
>> variation of that aspect and is only useful when also testing
>> for other aspects. Ignoring an aspect means using an
>> "unspecified_*" tag. For example, allowing a match for any
>> decoration requires using the <tt>unspecified_decoration</tt>
I have the following problems with this:
- it's too long for a single paragraph
- 80% focusses on a special case
- it's not enirely true that it is /only/ useful testing for other aspects
> In this paragraph, you are telling me that "ignoring an aspect" is
> "allow a match for any variation of that aspect" (sentence 2) and that
> "ignoring an aspect" is "using an "unspecified_*" tag" (sentence 3).
> The use of "means" in both sentences is awkward. It is also unclear
> that "allow a match for any variation of that aspect" is actually the
> same as "using an unspecified_* tag."
> I tend to be more conversational in my writing, but I would be tempted
> to write something like:
> When classifying types, it is often necessary to test for any one of
> several variations of an aspect. A common case is allowing a match for
> any variation of an aspect. This is done by ignoring that aspect and is
> implemented by using an "unspecified_*" tag. For example, to allow a
> For any decoration would require using the
> <tt>unspecified_decoration</tt> tag.
This one suffers similar problems (error propagation).
> I just wanted to throw in my $.02. I'll go back into lurker mode now.
Since my top-candidate is a different one (and the discussion on one paragraph
splinters too much to be helpful), I just posted an updated version of the whole
section on tag types.
I'ld really like to know if it works for you!
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