Beefy Boxes and Bandwidth Generously Provided by pair Networks
Perl: the Markov chain saw
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??
> Second, as long as we're working so hard to modify the parameter list, let's make the following a fatal error: swap( qw(this that) );

Thanks for pointing out this subtle difference!

After some meditation I actually I prefer this not being a fatal error!

The (lisp like) possibility of having references to literals always confused me to hell.

Back in time when LISP was running on 4 KB RAM it certainly made sense to avoid copies, but nowadays?

this little experiment shows whats happening when dereferencing a ref to a literal

$x=\1; $y=$$x; # equivalent to $y = 1, i.e. a copy $y++; print $y; #> 2

it's a copy and I thinks thats saner.

The other point is what a modifier-routine should return.

> But they all have a return value of the swapped list, so they're useful even when modifying the parameter list isn't the goal, right?

There are many possibilities:

- dual use by returning the swap => fault tolerance

- empty return to avoid double use => explicit use, ignore error

- carping if defined wantarray. => runtime warnings

But actually these design decisions are out of my scope, cause it doesn't inflict the idiom, cause it's the same problem when using $_[0] aliases etc.

for simplicity I'd simply add an empty return() to the example:

sub swap { my ($a, $b) = \(@_); ( $$a, $$b ) = ( $$b, $$a ); return; }

Cheers Rolf


In reply to Re^2: RFC: Idiom for named read-write arguments (aliases) instead of using $_[0] etc by LanX
in thread RFC: Idiom for named read-write arguments (aliases) instead of using $_[0] etc by LanX

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
  • Outside of code tags, you may need to use entities for some characters:
            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 rifling through the Monastery: (7)
    As of 2014-09-20 11:59 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      How do you remember the number of days in each month?











      Results (159 votes), past polls