Re: Is it a number?

[princepawn]

I remember in "Effective Perl Programming" merlyn did something like this:

$_ && bit_flip $_ eq "0"

Where bit_flip is something I forgot how to do in Perl.

Carter's compass: I know I'm on the right track when by deleting something, I'm adding functionality

[broquaint]

Ah yes, that would be

sub is_numeric {
  ($_[0] & ~ $_[0]) eq "0";
}

Which tests whether a scalar is a numeric value or a string value e.g 42 vs "42". Whereas the snippet discerns whether a given scalar looks like a number or not e.g

print +(isnum($_) ? "is a number" : "not a number"), ": $_", $/
  for qw( 1 2.2 3e3 4. .5);

__output__

is a number: 1
is a number: 2.2
is a number: 3e3
is a number: 4.
is a number: .5


HTH

_________
broquaint

[merlyn]

Yeah, the difference is the difference between "could this string be converted into a number without getting the warnings if -w is on?" vs "is this value always and only a number?". Everything in the latter case is also true for the former, but the inverse is not true. For example, all external data read from filehandles is always a string initially, so it could never pass this "is_numeric" test.