G'day seki,

Use of unary plus for disambiguation is common. Here's one instance in which I commonly use it:

$ perl -wE 'say (1 == 0) ? "Yes" : "No"'
say (...) interpreted as function at -e line 1.
Useless use of a constant ("Yes") in void context at -e line 1.
Useless use of a constant ("No") in void context at -e line 1.

$ perl -wE 'say +(1 == 0) ? "Yes" : "No"'
No
[download]

There's nothing special about say:

$ perl -wle 'print (1 == 0) ? "Yes" : "No"'
print (...) interpreted as function at -e line 1.
Useless use of a constant ("Yes") in void context at -e line 1.
Useless use of a constant ("No") in void context at -e line 1.

$ perl -wle 'print +(1 == 0) ? "Yes" : "No"'
No
$ perl -we 'printf (1 == 0) ? "Yes\n" : "No\n"'
printf (...) interpreted as function at -e line 1.
Useless use of a constant ("Yes\n") in void context at -e line 1.
Useless use of a constant ("No\n") in void context at -e line 1.
$ perl -we 'printf +(1 == 0) ? "Yes\n" : "No\n"'
No
[download]

There's also nothing special about the parenthesised list. Here, unary plus is used to disambiguate a hash key:

$ perl -wle 'use constant X => "x"; my %x = (x => 42); print $x{X}'
Use of uninitialized value in print at -e line 1.

$ perl -wle 'use constant X => "x"; my %x = (x => 42); print $x{+X}'
42
[download]

See the CAVEATS section of the constant pragma documentation for more on that.

It's also used to disambiguate a right brace starting a block from one starting a hashref. The map documentation has multiple examples of this.

"Has it a specific meaning there, or is it just an habit with a precise goal in everyday code?"

The code in question works with and without the unary plus:

$ perl -wE 'sub f { @_ } say f(42)'
42
$ perl -wE 'sub f { @_ } say+f(42)'
42
$ perl -wE 'sub f { @_ } say +f(42)'
42
[download]

And Perl sees such code as being identical (see B::Deparse if you're unfamiliar with the following usage):

$ perl -MO=Deparse,-p -e 'sub f { @_ } print f(42)'
sub f {
    @_;
}
print(f(42));
-e syntax OK
$ perl -MO=Deparse,-p -e 'sub f { @_ } print+f(42)'
sub f {
    @_;
}
print(f(42));
-e syntax OK
$ perl -MO=Deparse,-p -e 'sub f { @_ } print +f(42)'
sub f {
    @_;
}
print(f(42));
-e syntax OK
[download]

Of course, I can only guess at the original coders intentions:

• Could be force of habit.
• The author might be following some imposed coding standard.
• Perhaps the unary plus was originally needed; then, when the code changed, it was just left in.
• It might have been a typo which, causing no problems, raised no alarms during testing.
• And, of course, it could be something entirely different.

Finally, a friendly word of caution. You've received a number of replies: I strongly recommend that you take a quick look at "Worst Nodes" before deciding whose advice to take.

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

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! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, 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, summary, 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:
	&		&
	<		&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.