Warning-free numerification of a string

oxone has asked for the wisdom of the Perl Monks concerning the following question:

Monks - Any advice on a neat way to numerify any string under strictures without getting a warning?

I know that a string of chars will evaluate to zero in a numeric context, but it does so with a warning, eg.

use strict;
use warnings;

my $val1 = 'Test';
my $val2 = '5.6';

# $val1 += 0;    # How to numerify $val1 without a warning?

print "Sum is ", $val1 + $val2, "\n";
[download]

The example prints the right answer (5.6) but also issues a warning about the $val1 scalar being non-numeric. I've tried using +=0 and similar to safely numerify it first, but that gets me a warning too.

Is there a trick to doing that? Or it is a case of temporarily turning off warnings?

oxone | www.datasalon.com

Comment on Warning-free numerification of a string Download Code

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Re: Warning-free numerification of a string by Fletch (Bishop) on Aug 08, 2007 at 18:32 UTC
Perhaps use `looks_like_number` from Scalar::Util to check before you try to numify it? Besides that I think yes, you're going to have to do a `{ no warnings 'numeric'; ... }`.	[reply] [d/l] [select]
Re: Warning-free numerification of a string by clinton (Priest) on Aug 08, 2007 at 18:42 UTC
Why wouldn't it be a number? Presumably, because it is coming from outside, some uncontrolled source. So you should be checking that the input matches your expectations before processing it. This has the dual benefit of avoiding the warning, and making your program safer. Clint	[reply]
Re^2: Warning-free numerification of a string by oxone (Friar) on Aug 08, 2007 at 19:19 UTC
Sound advice ... now how would I go about "checking the input matches my expectations", those being that it should be a number, or else converted to zero (preferably without turning off warnings to do so). Ah yes, back to the original question then :-) oxone \| www.datasalon.com	[reply]
Re^3: Warning-free numerification of a string by clinton (Priest) on Aug 08, 2007 at 19:24 UTC
Either with Fletch's suggestion of `looks_like_number` from Scalar::Util, or a regex from Regexp::Common, or if actually, you're just expecting a positive integer, a simple regex like `/^\d*$/`	[reply] [d/l] [select]
Re: Warning-free numerification of a string by ikegami (Patriarch) on Aug 08, 2007 at 18:45 UTC
`for ($val1, $val2) { $_--; $_++; }` [download] works, at least for most values, but `for ($val1, $val2) { no warnings 'numeric'; $_ += 0; }` [download] is far less riskier and far more readable/maintainable.	[reply] [d/l] [select]
Re^2: Warning-free numerification of a string by oxone (Friar) on Aug 08, 2007 at 19:21 UTC
Thanks! Very sneaky, I like it. Probably a bit too sneaky to be considered maintainable, so I'll run with the latter. At least now I know I'm not missing a neat trick here. oxone \| www.datasalon.com	[reply]
Re^3: Warning-free numerification of a string by syphilis (Archbishop) on Aug 09, 2007 at 03:02 UTC
If `$_` is a string that that does not `look_like_number()`, then don't be fooled into thinking that `$_ + 0` will inevitably evaluate to zero: `$_ = '12*&&#$%'; $_ += 0; print $_, "\n"; # prints 12` [download] Cheers, Rob	[reply] [d/l] [select]
Re^3: Warning-free numerification of a string by varian (Chaplain) on Aug 08, 2007 at 22:09 UTC
Not sneaky at all, just contain the no-warnings to where you need it and the requirement is crystal-clear: `{ no warnings 'numeric'; $val1 = $val1+0; # force numeric }` [download]	[reply] [d/l]