Deparse shows that the parentheses in the OP are unnecessary, which is as expected, since the conditional operator ?: has a higher precedence than assignment (see Operator Precedence and Associativity). Consider:
#! perl
use strict;
use warnings;
my @x = qw(Initial list of words 1);
my $y = 'Initial string 1';
show('With parentheses');
my @z = ( time() ? @x = qw(Words_z from conditional) : $y ) = foo();
print "\@z = (@z)\n";
show('After assignment to LHS');
@x = qw(Initial list of words 2);
$y = 'Initial string 2';
show('Without parentheses');
my @w = time() ? @x = qw(Words_w from conditional) : $y = foo();
print "\@w = (@w)\n";
show('After assignment to LHS');
sub foo
{
if (wantarray())
{
print "\nfoo called in list context\n";
return qw(sub_foo word list);
}
else
{
print "\nfoo called in scalar context\n";
return 'String_from_foo';
}
}
sub show
{
my ($heading) = @_;
print "\n$heading:\n\n";
print "\@x = (@x)\n";
print "\$y = '$y'\n";
}
Output:
17:35 >perl 678_SoPW.pl
With parentheses:
@x = (Initial list of words 1)
$y = 'Initial string 1'
foo called in scalar context
@z = (String_from_foo)
After assignment to LHS:
@x = (Words_z from conditional)
$y = 'Initial string 1'
Without parentheses:
@x = (Initial list of words 2)
$y = 'Initial string 2'
foo called in scalar context
@w = (String_from_foo)
After assignment to LHS:
@x = (Words_w from conditional)
$y = 'Initial string 2'
17:35 >perl -v
This is perl 5, version 18, subversion 0 (v5.18.0) built for MSWin32-x
+86-multi-thread-64int
It’s clear that foo is being evaluated in scalar context, even though the condition evaluates to true and so chooses the LHS. Since foo would still be evaluated in scalar context if the condition were false and the RHS chosen, it’s now clear why the compile error has disappeared: it is known at compile time that foo will be evaluated in scalar context.
But that leaves us with some unanswered questions:
- What exactly is the l-value returned by the conditional expression?
- Why does this l-value — which results from the assignment of a list to an array — put foo into scalar context?
- Why does the assignment to @x seemingly occur after the call to foo?
I have the feeling that there’s an obvious answer to all this, but I can’t see it. Which is, just possibly, related to the fact that in my neck of the woods the Ashes coverage finishes around 3:30 am... |-O
-
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 How to display code and escape characters
are good places to start.
|