Other than throwing an exception during the execution of an object's
constructor, is there any way to cancel creation of the object in such a
way that it leaves a reference to it null or undefined. That would enable
the simple test:
var ref = new someObject();
if( ref ) {
// Object created successfully
}
I know one could use state flags instead, but the object I have in mind
shouldn't exist if the arguments passed to it are incorrect (there is a
good reason, trust me).
[OT - Exceptions in general (including other languages)]
Some people seem to have issues concerning throwing an exception during
object construction to signify failure and instead prefer to use state
flags. Any thoughts either way?
[/OT]
By the way, it's not possible to have protected[1] members in JavaScript,
is it? Shame...
Many thanks,
Mike
[1] I do mean protected, not private.
--
Michael Winter M.******@blueyo nder.co.invalid (replace ".invalid" with ".uk" to reply)
Jul 20 '05
16  1369 
On Tue, 02 Mar 2004 18:40:55 +0100, Lasse Reichstein Nielsen
<lr*@hotpop.com > wrote: "Richard Cornford" <Ri*****@litote s.demon.co.uk> writes:
Richard Cornford wrote:
<snip> ... (I have got a copy of the 3nd edition of ECMA 262
^
That should have been 2nd edition.
I was about to say "me too", but found that it can be downloaded
at <URL:http://www.mozilla.org/js/language/> (along with version 1).
Thank you, both of you.
It's strange that the earlier editions aren't available from the ECMA
website, or that changes between versions aren't marked.
I do have the 3rd edition, but I can rarely make heads or tails of it. It
must be the worst written, yet grammatically-correct document I've ever
read. I find it odd that that level of incomprehensibi lity is acceptable
to the authors. I would have thought that the aim of the document would be
to explain the language to anyone who wishes to use it, as other language
specifications attempt to do. I'm not too sure who that document is geared
towards. It certainly isn't at a level that the casual script author can
use. Compare it to the Java Language Specification, for example.
Richard: Thank you for your explanation of protected members in
JavaScript, and for the comments on my proposed approach. I guessed that
there would be problems, but I didn't think that it would be with the
availability of instanceof (it was introduced in v1.4 with exceptions). I
won't be able to review the code you presented tonight, but I will
tomorrow.
Mike
--
Michael Winter M.******@blueyo nder.co.invalid (replace ".invalid" with ".uk" to reply)
On Tue, 02 Mar 2004 12:55:33 -0500, Randy Webb <hi************ @aol.com>
wrote: Richard Cornford wrote:
(I have got a copy of the 3nd edition of ECMA 262
which I could e-mail you if you are interested)
I am please.
You can obtain the 3rd Ed. directly from ECMA for free as a PDF: http://www.ecma-international.org/pu...s/Ecma-262.htm
Mike
--
Michael Winter M.******@blueyo nder.co.invalid (replace ".invalid" with ".uk" to reply)
Michael Winter wrote: On Tue, 02 Mar 2004 12:55:33 -0500, Randy Webb <hi************ @aol.com>
wrote:
Richard Cornford wrote:
(I have got a copy of the 3nd edition of ECMA 262
which I could e-mail you if you are interested)
I am please.
You can obtain the 3rd Ed. directly from ECMA for free as a PDF:
http://www.ecma-international.org/pu...s/Ecma-262.htm
Thanks Mike. I saw Lasse's post after I replied and have them both book
marked now :-)
--
Randy
Chance Favors The Prepared Mind
comp.lang.javas cript FAQ - http://jibbering.com/faq/
Michael Winter <M.******@bluey onder.co.invali d> writes: I do have the 3rd edition, but I can rarely make heads or tails of
it. It must be the worst written, yet grammatically-correct document
I've ever read.
I have seen worse :)
I find it odd that that level of incomprehensibi lity
is acceptable to the authors. I would have thought that the aim of the
document would be to explain the language to anyone who wishes to use
it, as other language specifications attempt to do.
I disagree. The purpose of a language specification is to define the
language unambiguously and exactly. It is not a tutorial, it is a
reference document. Adding too much explanation text risks adding
ambiguiuity either in the text or between the text and the formal
specification.
Ofcourse, there should also be a tutorial, but I guess ECMA left that
to the Netscape and Microsoft Corporations or other implementors of
the language.
I'm not too sure who that document is geared towards. It certainly
isn't at a level that the casual script author can use.
Compare it to the Java Language Specification, for example.
Ok, ECMAScript is not exactly easy to read :) I admit that the JLS
is easier to read, although it too can get pretty hard too.
Is it also as complete, including the behavior of all build-in
functions?
Now compare it to the R5RS
<URL:http://www.swiss.ai.mi t.edu/~jaffer/r5rs_toc.html>
/L
--
Lasse Reichstein Nielsen - lr*@hotpop.com
DHTML Death Colors: <URL:http://www.infimum.dk/HTML/rasterTriangleD OM.html>
'Faith without judgement merely degrades the spirit divine.'
On Tue, 02 Mar 2004 19:29:48 +0100, Lasse Reichstein Nielsen
<lr*@hotpop.com > wrote: Michael Winter <M.******@bluey onder.co.invali d> writes:
I do have the 3rd edition, but I can rarely make heads or tails of
it. It must be the worst written, yet grammatically-correct document
I've ever read.
I have seen worse :)
I don't doubt that.
I find it odd that that level of incomprehensibi lity
is acceptable to the authors. I would have thought that the aim of the
document would be to explain the language to anyone who wishes to use
it, as other language specifications attempt to do.
I disagree. The purpose of a language specification is to define the
language unambiguously and exactly. It is not a tutorial, it is a
reference document. Adding too much explanation text risks adding
ambiguiuity either in the text or between the text and the formal
specification.
It would depend on who is the target audience. The Standard doesn't say,
but it does seem that, due to the detail in how methods are implemented,
writers of a JavaScript interpreter are the most likely.
Ofcourse, there should also be a tutorial, but I guess ECMA left that
to the Netscape and Microsoft Corporations or other implementors of
the language.
I don't find that the Netscape and Microsoft references are always
sufficient. For the most part, they are fine, but I would like something
between them and ECMA-262.
I'm not too sure who that document is geared towards. It certainly
isn't at a level that the casual script author can use.
Compare it to the Java Language Specification, for example.
Ok, ECMAScript is not exactly easy to read :) I admit that the JLS
is easier to read, although it too can get pretty hard too.
Is it also as complete, including the behavior of all build-in
functions?
I can't say for certain. It has been a year since I read it properly (I
went front-to-back then). However, if memory serves, the grammar of the
language is fully specified. Multi-threading issues are covered to a level
where a conforming implementation could be built. I think even the loading
of class files is covered.
Perhaps the difference between them is that Sun provide the run-time
engine for virtually every operating system, so no implementations need to
be made. That allows the specification to concentrate on language itself,
and not its internal behaviour. If ECMA-262 contained some additional
comments that summarise the processes described, it would be a good step
forward. This would allow both precision and comprehension.
Now compare it to the R5RS
<URL:http://www.swiss.ai.mi t.edu/~jaffer/r5rs_toc.html>
In what regard: specificity or ease of reading?
With the former, it appears to be about equal to JLS. Somewhat more
verbose, perhaps, but not radically different.
With the latter, I can't honestly say without reading and understanding a
good proportion of the text which I haven't had the time to do, and have
no inclination to do at this time of night :) Superficially, it is easier
to comprehend than ECMA-262.
The two major stumbling blocks I have are the indirect method of
description, and the choice of language. The specification seems to be
written with an incremental approach, where parts of an explanation rely
heavily on previous topics (the definition of some basic functions, for
example). This gives the impression that one must virtually memorise the
first few sections before even considering the use of the remaining
document, which makes it useless (for me) for a reference. The language is
a minor problem in comparison. To illustrate that, the only example I
could find after a quick search is the use of "Disjunctio n" instead of
"Separator" in the grammar for regular expression patterns.
Perhaps, at some point, I should read the whole thing slowly, rather than
to try and use it to understand certain elements of the language.
Mike
--
Michael Winter M.******@blueyo nder.co.invalid (replace ".invalid" with ".uk" to reply)
This is incorrect, JS does not support protected members.
George Jempty <fl********@bel lsouth.net> wrote in message news:<mO******* **********@bign ews4.bellsouth. net>... <snip>
By the way, it's not possible to have protected[1] members in
JavaScript, is it? Shame...
No, this is one of the great fallacies about Javascript. Javascript
supports closures and therefore supports protected/private members. See:
http://www.crockford.com/javascript/private.html
> This is incorrect, JS does not support protected members.
Java needs protected members to compensate for the brittleness of the
classical object model. JavaScript is class-free, and so does not need
them. See http://www.crockford.com/javascript/inheritance.html This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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