Re: Understanding &&

From	Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups	comp.lang.javascript
Subject	Re: Understanding &&
Date	2021-04-19 23:13 +0100
Organization	A noiseless patient Spider
Message-ID	<87fszlzzw9.fsf@bsb.me.uk> (permalink)
References	(5 earlier) <ie16fpFavc9U1@mid.individual.net> <87lf9ga4gz.fsf@bsb.me.uk> <ie58ilF4ao6U1@mid.individual.net> <87r1j6yq6u.fsf@bsb.me.uk> <slrns7rv41.6lk.jon+usenet@raven.unequivocal.eu>

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Jon Ribbens <jon+usenet@unequivocal.eu> writes:

> On 2021-04-19, Ben Bacarisse <ben.usenet@bsb.me.uk> wrote:
>> Arno Welzel <usenet@arnowelzel.de> writes:
>>> 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
>>
>> OK, I see what you mean.  I disagree, but I'm not sure that it matters
>> enough to say much about it.  Bottom line: programmer should know the
>> language, and the language does guarantee what you think of as a
>> convention.
>>
>>> return
>>>   statement1 &&
>>>   statement2 &&
>>>   statement3 &&
>>>   statement4;
>>
>> (Odd terminology.  These have to expressions, not statements.)
>>
>>> 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.
>>
>> Need three more lines:
>>
>>   if (!statement1) {
>>     return false;
>>   }
>>   if (!statement2) {
>>     return false;
>>   }
>>   if (!statement3) {
>>     return false;
>>   }
>>   if (!statement4) {
>>     return false;
>>   }
>>   return true;
>>
>> You could write return !!statement4; or return statement4 == true; but I
>> assume you'd rather keep the pattern going.
>
> You're kinda disproving your own point here though, since you're the one
> claiming that the boolean expression is easy for you to understand, but
> you don't actually know what it does - in fact both your and Arno's
> versions are wrong:

Touché.  I was forgetting what language this was.  This topic comes up
every year or so in comp.lang.c.

But I don't think I'm making your case.  I'm making mine.  Programmers
should learn the language!

>   return statement1 && statement2 && statement3 && statement4
>
> is not equivalent to either of the above, it is equivalent to:
>
>   if (!(temp = statement1)) return temp
>   if (!(temp = statement2)) return temp
>   if (!(temp = statement3)) return temp
>   return statement4

-- 
Ben.

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Thread

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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