Scalar::Util::looks_like_number

By Steven Haryanto on October 18, 2013 11:02 AM

I had a recent discussion with a Data::Dump::Color user about formatting ints/floats/stringy numbers differently. So here's a short summary of how core module function Scalar::Util's looks_like_number() can be used to detect the different data types:

perl -MScalar::Util=looks_like_number \
-E'printf "%6d # %s\n", $l=looks_like_number($_), $l<20?qq("$_"):$_ 
for ("str", 0, 1, "1", "1a", -1, "-1", 0.1, "0.1", -0.1, "-0.1", 1e20, nan, -nan, inf, -inf)'
     0 # "str"
  4352 # 0
  4352 # 1
     1 # "1"
     0 # "1a"
  4352 # -1
     9 # "-1"
  8704 # 0.1
     5 # "0.1"
  8704 # -0.1
    13 # "-0.1"
  8704 # 1e+20
    36 # nan
    44 # -nan
    20 # inf
    28 # -inf

4 comments

4 Comments

Toby Inkster | October 18, 2013 2:37 PM | Reply

Interestingly, on the stock Scalar::Util that comes with newer versions of Perl, looks_like_number(undef) => 0 but on very old versions (such as that bundled with Perl 5.8.1) looks_like_number(undef) => 1.

Steven Haryanto replied to comment from Toby Inkster | April 17, 2014 9:41 AM | Reply

BTW, it looks like maybe looks_like_number() will return canonical bool, so all this might be going away soon:

https://rt.cpan.org/Ticket/Display.html?id=94805

By then we'll need Scalar::Util (or some other module) to provide things like is_nan() (or looks_like_nan(), whatever), is_inf(), is_stringy_num(), is_stringy_int(), is_stringy_float(), etc.

But it's convenient to be able to differentiate different types of numbers in a single call though.

Steven Haryanto | June 30, 2014 7:44 PM | Reply

https://rt.cpan.org/Ticket/Display.html?id=94806

A new version of Scalar::Util has been released and now booleanizes looks_like_number(), so this trick can no longer be used. As an alternative, see chocolateboy's Scalar::Util::Numeric.

Steven Haryanto | June 30, 2014 7:58 PM | Reply

https://github.com/sharyanto/scripts/blob/master/list-numeric-scalar-types

Sample output (hopefully MT will behave here):

looks_like_number (Scalar::Util 1.39): 'inf' 1 'nan' 1 '-inf' 1 1 1 '1' 1 '1.2' 1 '1.2' 1 -1 1 '-1.2' 1 '-1' 1 '-1.2' 1 '1e+100' 1 '1e-100' 1 'a' 0

Scalar::Util::Numeric:
value isnum isint isuv isbig isfloat isneg isinf isnan
'inf' 20 0 0 0 1 0 1 0
'nan' 36 0 0 0 1 0 0 1
'-inf' 28 0 0 0 1 1 1 0
1 1 1 1 0 0 0 0 0
'1' 1 1 1 0 0 0 0 0
'1.2' 5 0 1 0 1 0 0 0
'1.2' 5 0 1 0 1 0 0 0
-1 9 -1 1 0 0 1 0 0
'-1.2' 13 0 1 0 1 1 0 0
'-1' 9 -1 1 0 0 1 0 0
'-1.2' 13 0 1 0 1 1 0 0
'1e+100' 4 0 0 0 1 0 0 0
'1e-100' 4 0 0 0 1 0 0 0
'a' 0 0 0 0 0 0 0 0

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About Steven Haryanto

A programmer (mostly Perl 5 nowadays). My CPAN ID: SHARYANTO. I'm sedusedan on perlmonks. My twitter is stevenharyanto (but I don't tweet much). Follow me on github: sharyanto.

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