Beefy Boxes and Bandwidth Generously Provided by pair Networks
Your skill will accomplish
what the force of many cannot
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??
But, having dug in to Perl Guts more than I should have, I think that disallowing tied (and probably other magic) variables on the RHS, a built-in smart match would be able to reliably determine if the RHS is a number.

The problem is that Perl doesn't expose the concept "this scalar is a number" to the user (by design). Thus making a decision based on whether a scalar is a number is nearly always wrong.

A piece of code that already makes such a decision is the code that decides whether to warn on a numeric operation:

$ perl -wE 'say 0 + "1.2"' 1.2 $ perl -wE 'say 0 + "1.2.3"' Argument "1.2.3" isn't numeric in addition (+) at -e line 1. 1.2

So, what do I keep complaining about? A real problem are dual vars. Those aren't just a rare corner case that should be avoided, but for example the result from boolean operators:

$ perl -wE 'say 0 + !1' # no warning 0 $ perl -wE 'my $false = !1; say "<<$false>>"' # empty string! <<>>

So it's a number, but it's also an empty string. Should smart-matching against that be numeric or string comparison? My intuitive reaction is "string comparison", because $false doesn't round-trip when converted to a number and then to a string.

But you can also construct valid cases where round-tripping to a number is the wrong criterion; an example is if a user-supplied string is never used as a number, but happens to look like a number. You certainly don't want those values to try to coerce your own strings to numbers (and warn).

So, however you decide whether a scalar is number or a string for the purpose of comparision, I can point out a case where your decision is a big WTF. Which is precisely the reason that we have separate == and eq operators.

Whatever will be done about that, the string/number duality will remain a weakness of any Perl 5 smartmatch proposal.


In reply to Re^3: Bring back the smartmatch operator (but with sane semantics this time)! by moritz
in thread Bring back the smartmatch operator (but with sane semantics this time)! by smls

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others meditating upon the Monastery: (10)
    As of 2015-07-06 19:49 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      The top three priorities of my open tasks are (in descending order of likelihood to be worked on) ...









      Results (81 votes), past polls