Re: Failure in commit_ts tap tests

On Sat, Jan 21, 2017 at 9:39 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

> Pavan Deolasee <pavan.deolasee@gmail.com> writes:
> > On Sat, Jan 21, 2017 at 9:09 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >> Hm, but what of the "null" value?  Also, I get
> >>
> >> $ perl -e 'use warnings; use Test::More; ok("2017-01-01" != "null",
> "ok");'
> >> Argument "null" isn't numeric in numeric ne (!=) at -e line 1.
> >> Argument "2017-01-01" isn't numeric in numeric ne (!=) at -e line 1.
> >> ok 1 - ok
>
> > It declares the test as "passed", right?
>
> Oh!  So it does.  That is one darn weird behavior of the != operator.
>
>
Indeed! See this:

# first numeric matches, doesn't check beyond that
$ perl -e 'if ("2017-23" != "2017-24") {print "Not equal\n"} else {print
"Equal\n"}'
Equal

# first numeric doesn't match, operators works ok
$ perl -e 'if ("2017-23" != "2018-24") {print "Not equal\n"} else {print
"Equal\n"}'
Not equal

# comparison of numeric with non-numeric, works ok
$ perl -e 'if ("2017-23" != "Foo") {print "Not equal\n"} else {print
"Equal\n"}'
Not equal

# numeric on RHS, works ok
$ perl -e 'if ("Foo" != "2018-24") {print "Not equal\n"} else {print
"Equal\n"}'
Not equal

These tests show that the operator returns the correct result it finds a
numeric value at the start of the string, either on LHS or RHS. Also, it
will only compare the numeric values until first non-numeric character is
found.

# no numeric on either side
$ perl -e 'if ("Fri 2017-23" != "Fri 2017-23") {print "Not equal\n"} else
{print "Equal\n"}'
Equal

*# no numeric on either side, arbitrary strings declared as equal*
$ perl -e 'if ("Fri 2017-23" != "Foo") {print "Not equal\n"} else {print
"Equal\n"}'
Equal

These two tests show why we saw no failure earlier. If neither LHS or RHS
string has a starting numeric value, the operator declares the arguments as
equal, irrespective of their values. I tested the same with == operator and
that also exhibits the same behaviour. Weird and I wonder how it's not a
source of constant bugs in perl code (I don't use perl a lot, so may be
those who do are used to either turning warnings on or know this already.


>
>
> There's still the point that we're not actually exercising this script
> in the buildfarm ...
>

Yes indeed.

Thanks,
Pavan

-- 
 Pavan Deolasee                   http://www.2ndQuadrant.com/
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