On 06 Dec 2008, at 20:38, Warren DeLano wrote:
Date: Fri, 05 Dec 2008 22:22:38 -0800
From: Dennis Lee Bieber <[EMAIL PROTECTED]>
Subject: Re: "as" keyword woes
To: [EMAIL PROTECTED]
Message-ID: <[EMAIL PROTECTED]>
I'm still in the dark as to what type of data could
even inspire the
use of "as" as an object name... A collection of "a" objects? In
which
case, what are the "a"s? <G>
Please let me clarify. It is not "as" as a standalone object that we
specifically miss in 2.6/3, but rather, the ability to use ".as"
used as
a method or attribute name.
In other words we have lost the ability to refer to "as" as the
generalized OOP-compliant/syntax-independent method name for casting:
new_object = old_object.as(class_hint)
# For example:
float_obj = int_obj.as("float")
# or
float_obj = int_obj.as(float_class)
# as opposed to something like
float_obj = int_obj.asFloat()
# which requires a separate method for each cast, or
float_obj = (float)int_obj
# which required syntax-dependent casting [language-based rather than
object-based].
Of course, use of explicit casting syntax "(float)" is fine if you're
restricting yourself to Python and other languages which support
casting, but that solution is unavailable inside of a pure OOP
message-passing paradigm where object.method(argument) invocations are
all you have to work with.
Please note that use of object.asClassname(...) is a ubiqitous
convention for casting objects to specific classes (seen in
ObjectiveC,
Java, SmallTalk, etc.).
There, I assert that 'object.as(class_reference)' is the simplest and
most elegant generalization of this widely-used convention. Indeed,
it
is the only obvious concise answer, if you are limited to using
methods
for casting.
Although there are other valid domain-specific uses for "as" as
either a
local variable or attribute names (e.g. systematic naming: as, bs,
cs),
those aren't nearly as important compared to "as" being available as
the
name of a generalized casting method -- one that is now strictly
denied
to users of Python 2.6 and 3.
As someone somewhat knowledgable of how parsers work, I do not
understand why a method/attribute name "object_name.as(...)" must
necessarily conflict with a standalone keyword " as ". It seems to me
that it should be possible to unambiguously separate the two without
ambiguity or undue complication of the parser.
So, assuming I now wish to propose a corrective PEP to remedy this
situation for Python 3.1 and beyond, what is the best way to get
started
on such a proposal?
Cheers,
Warren
As long as "as" is widely known as a keyword, I don't see the problem.
Every python developer knows that the convention is to add a trailing
underscore when you want to use a reserved word in your code. Besides,
your examples are quite abstract. I'm sure it's possible to find good
examples for "while", "with", "import", "from" (I often use "from_")
or "try" as well. Or perhaps that the python keywords should be "as_"
so we leave "as" free for eventual methods?
As for the implicit proposition of allowing keywords only for methods,
I agree with Guido about it being a slippery slope. So we would end up
with a language where it is allowed to name methods after keywords,
but not functions (they can be declared in the local scope)? Yikes! Oh
well, maybe it's possible for an intelligent parser to distinguish
between keywords and function references, but think of the poor
grammar highlighters in all source editors! What a nightmare it will
be for them. Anyway, is there any language that does this, allowing
keywords as method names? I don't know, but if not, there's probably a
reason for it.
Your views on code elegance are also rather Javaish. I'd go for
"class_reference(object)" (and why the heck would you "be limited to
using method for casting"?).
Ciao,
Virgil
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