Beefy Boxes and Bandwidth Generously Provided by pair Networks
good chemistry is complicated,
and a little bit messy -LW
 
PerlMonks  

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??

After reading Conditional Operator, and delighting in the potential for unreadable code coming from using a conditional operator as an lvalue, I wondered how far in advance the lvalues have to be declared.

Huh? Well, we know that

my ( $c, $d ); 1 ? $c : $d = 'Hi';
is the same (to B::Deparse) as
my ( $c, $d ); $c = 'Hi';
but what if you don't want to declare the variables in advance? Well,
my $d; 1 ? my $c : $d = 'Hi';
is the same as
my $d; my $c = 'Hi';
In the other direction, here's a strict-safe program that B::Deparse makes non-strict-safe:
$ perl -MO=Deparse -e 'my $c; 1 ? $c : my $d; $d' my $c; $c; $d; -e syntax OK
*. How about if we declare both variables in the conditional?
$ perl -e '1 ? my $c : my $d' Invalid separator character '$' in attribute list at -e line 1, near " +$c : my " Execution of -e aborted due to compilation errors.
Now, maybe there's some reason that parsing : my $d as an attribute list is good, or at least expected; but I can't see why 1 ? my $c : my $d would be parsed that way, but 1 ? my $c : $d wouldn't. Would somemonk enlighten me?

UPDATE: * Notice that B::Deparse changes the semantics here (but I guess there's always the disclaimer that that might happen). For example,

our $d = 'Out'; { 1 ? 0 : my $d; $d = 'In'; } say $d;
prints Out, but is converted by B::Deparse into
our $d = 'Out'; { '???'; $d = 'In'; } say $d;
which prints In.

UPDATE: Oh, maybe it's that a colon followed by whitespace and an alphanumeric is always interpreted as the beginning of an attribute list, even if we're waiting for the interstitial colon of a conditional operator. Is this correct? If so, is it the desired behaviour? If so, should the precedence table in perlop be changed to reflect it?


In reply to Unexpected parsing by JadeNB

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



  • Are you posting in the right place? Check out Where do I post X? to know for sure.
  • Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
    <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
  • Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
  • Want more info? How to link or or How to display code and escape characters are good places to start.
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 examining the Monastery: (4)
As of 2021-05-13 06:27 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?
    Perl 7 will be out ...





    Results (134 votes). Check out past polls.

    Notices?