I’m puzzled by the behaviour in the following run. I would expect line 2
to not print out “ouch” because the result of the if statement is 0
(verified online 8)
$ ruby -v
ruby 1.7.3 (2002-09-20) [i386-cygwin]
$ irb
irb(main):001:0> data = 0x00
0
irb(main):002:0> puts “ouch” if (data & 0x80)
ouch
nil
irb(main):003:0> puts “ouch” if (data & 0x80) != 0
nil
irb(main):004:0> data = 0x90
144
irb(main):005:0> puts “ouch” if (data & 0x80)
ouch
nil
irb(main):006:0> puts “ouch” if (data & 0x80) != 0
ouch
nil
irb(main):007:0> data = 0x00
0
irb(main):008:0> data & 0x80
0
irb(main):009:0>
Rob
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I’m puzzled by the behaviour in the following run. I would expect line 2
to not print out “ouch” because the result of the if statement is 0
(verified online 8)
$ ruby -v
ruby 1.7.3 (2002-09-20) [i386-cygwin]
$ irb
irb(main):001:0> data = 0x00
0
irb(main):002:0> puts “ouch” if (data & 0x80)
ouch
I’m puzzled by the behaviour in the following run. I would expect line 2
to not print out “ouch” because the result of the if statement is 0
(verified online 8)
$ irb
irb(main):001:0> data = 0x00
0
irb(main):002:0> puts “ouch” if (data & 0x80)
ouch
$ irb
irb(main):001:0> data = 0x00
0
irb(main):002:0> puts “ouch” if (data & 0x80)
ouch
Don’t forget that 0 is true.
Duh, thank you, I had compelely forgotten that.
I still find myself easily slipping into “other language mode”.
Rob
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Er… Not that I couldn’t fix my scripts (my server monitor
just stopped alerting me of a recent downtime exactly for
this mistake…), but, Matz, is “if 0” being the same as
“if true” your final word on this?
Better to say “everything is true except nil and false” rather than
“everything is true except nil, false, zero (integer, not float), and
the empty string, except when the objects happen to be hidden behind a
proxy or alternative implementation”. No?
···
Szabolcs Szasz (sz@szasz.hu) wrote:
Er… Not that I couldn’t fix my scripts (my server monitor just
stopped alerting me of a recent downtime exactly for this mistake…),
but, Matz, is “if 0” being the same as “if true” your final word on
this?
One of the things I find annoying about Perl is having to write everywhere
if (defined $x)
or if (exists $x{$y})
because 'if ($x)' introduces subtle special-case bugs (where $x is a string
containing exactly "0", for example) - and I see many examples of code which
is broken in this way. IMO those surprises, in 0.01% of cases, are far more
annoying and difficult to track down than something which persistently fails
simply because the language does not do what a 'C' programmer would expect.
Also, bitwise tests don't occur very frequently. I'd be quite happy to write
puts "yippee" if (data & 0x80) == 0
and it makes the intention very clear.
Perhaps it would be helpful if ruby -w generated a warning if a Fixnum is
used as a truth value; that would force you to write
if myint != 0
(However, if you don't know the type of an object in advance you could
also be forced to write 'unless param.nil?' instead of 'if param' to
avoid this warning, which takes us back to the Perl situation)
Regards,
Brian.
···
On Tue, Oct 15, 2002 at 06:43:53AM +0900, Szabolcs Szasz wrote:
> > Don't forget that 0 is true.
>
> Duh, thank you, I had compelely forgotten that.
Er... Not that I couldn't fix my scripts (my server monitor
just stopped alerting me of a recent downtime exactly for
this mistake...), but, Matz, is "if 0" being the same as
"if true" your final word on this?
