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Groups > comp.lang.javascript > #39982
| From | Arno Welzel <usenet@arnowelzel.de> |
|---|---|
| Newsgroups | comp.lang.javascript |
| Subject | Re: Understanding && |
| Date | 2021-04-19 13:41 +0200 |
| Message-ID | <ie58ilF4ao6U1@mid.individual.net> (permalink) |
| References | (2 earlier) <87wnt2e06e.fsf@bsb.me.uk> <slrns7jb5v.4j8.jon+usenet@raven.unequivocal.eu> <87mttydm95.fsf@bsb.me.uk> <ie16fpFavc9U1@mid.individual.net> <87lf9ga4gz.fsf@bsb.me.uk> |
Ben Bacarisse:
> Arno Welzel <usenet@arnowelzel.de> writes:
[...]
>> x = a && b;
>>
>> Nobody would expect that this *expression* will cause parts of the code
>> to get executed or not
>
> Hmm... Everyone should expect that since that's what && means. Do you
> mean && (as defined) should simply not exist is programming languages?
No. It is just what I said - "a && b" is an expression which will not
change anything in a or b because there is no additional code getting
executed which might change a or b depending on the value of a.
[...]
>> The ??= operator was *intentionally* designed to work this way.
>
> That's a new one to me. I thought the 11th edition was the latest, and
> it's not in there.
I maybe got ??= from another language, I can't remember where I looked
this up when I mentioned it, sorry. Just forget it.
> That aside, I think && and || were intentionally designed to work as
> they do, so intentional design can't justification enough in your mind.
Ok, I need to clarify this:
For an expression like "a && b" or "a || b" there is no obvious way how
it will get evaluated. It's just a convetion that the evaluation will
stop at the point where the remaining part does not *need* to be evaluated.
a && b will evualate "a" first and stop, if a is false
a || b will evualate "a" first and stop, if a is true
But this is something one needs to know besides the fact that "&&" means
"logical and" and "||" means "logical or". Therefore I call i at least
bad style to rely on this fact and create code like
return
statement1 &&
statement2 &&
statement3 &&
statement4;
instead of
if (!statement1) {
return false;
}
if (!statement2) {
return false;
}
if (!statement3) {
return false;
}
return statement 4;
Yes, the latter one needs more lines but is obvious what the code does
even if you don't remember that "&&" is evaluated from left to right and
that the the evaluation stops at the first statement which returns false.
--
Arno Welzel
https://arnowelzel.de
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Understanding && Andrew Poulos <ap_prog@hotmail.com> - 2021-04-16 14:30 +1000
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-16 11:00 +0100
Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-16 11:17 +0000
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-16 16:09 +0100
Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-16 15:26 +0000
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-16 21:09 +0100
Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-16 21:06 +0000
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-17 02:01 +0100
Re: Understanding && The Natural Philosopher <tnp@invalid.invalid> - 2021-04-17 08:33 +0100
Re: Understanding && John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-17 12:06 +0100
Re: Understanding && The Natural Philosopher <tnp@invalid.invalid> - 2021-04-17 14:13 +0100
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-17 15:50 +0100
Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-17 15:21 +0000
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-17 23:46 +0100
Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-17 23:46 +0000
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-18 23:59 +0100
Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-19 13:56 +0000
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-19 23:08 +0100
Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-19 22:52 +0000
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-20 01:23 +0100
Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-20 01:08 +0000
Re: Understanding && Arno Welzel <usenet@arnowelzel.de> - 2021-04-18 00:49 +0200
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-18 17:26 +0100
Re: Understanding && Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2021-04-17 17:05 +0200
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-17 23:04 +0100
Re: Understanding && Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2021-04-18 00:48 +0200
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-18 17:13 +0100
Re: Understanding && Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2021-04-19 21:58 +0200
Re: Understanding && John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-18 18:20 +0100
Re: Understanding && Arno Welzel <usenet@arnowelzel.de> - 2021-04-18 00:40 +0200
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-18 00:14 +0100
Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-18 00:01 +0000
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-18 17:44 +0100
Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-18 17:51 +0000
Re: Understanding && Arno Welzel <usenet@arnowelzel.de> - 2021-04-19 13:41 +0200
Re: Understanding && John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-19 15:02 +0100
Re: Understanding && The Natural Philosopher <tnp@invalid.invalid> - 2021-04-20 17:40 +0100
Re: Understanding && John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-20 18:19 +0100
Re: Understanding && The Natural Philosopher <tnp@invalid.invalid> - 2021-04-21 10:11 +0100
Re: Understanding && John G Harris <niam@jghnorth.org.uk.invalid> - 2021-04-21 19:46 +0100
Re: Understanding && The Natural Philosopher <tnp@invalid.invalid> - 2021-04-22 13:48 +0100
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-19 21:28 +0100
Re: Understanding && Jon Ribbens <jon+usenet@unequivocal.eu> - 2021-04-19 21:56 +0000
Re: Understanding && Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-04-19 23:13 +0100
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