Beefy Boxes and Bandwidth Generously Provided by pair Networks
Perl Monk, Perl Meditation
 
PerlMonks  

Re^4: printing unitialized value of the 'do BLOCK'

by rsFalse (Chaplain)
on Dec 23, 2019 at 08:22 UTC ( [id://11110538]=note: print w/replies, xml ) Need Help??


in reply to Re^3: printing unitialized value of the 'do BLOCK'
in thread printing unitialized value of the 'do BLOCK'

Hey!

So it means that an 'if' statement in function/RHS context returns the last expression evaluated! And this isn't documented I guess.
I guess newcomer would expect to get a 1 or ''/0 as a return value of 'if', but he can get also an 'undefined'. E.g. print do { 3 if undef };

.=
Interestingly, only one of these lines gives a warning: 
print do { 3 if () };
print do { () };

[download]

Replies are listed 'Best First'.
Re^5: printing unitialized value of the 'do BLOCK'
by LanX (Saint) on Dec 23, 2019 at 12:54 UTC
    > Interestingly, only one of these lines gives a warning:

    because the second one returns an empty list, which is a legal use of print.

    C:\WINDOWS\system32>Perl -MData::Dump=pp -e "pp do{3 if ()} "
undef

C:\WINDOWS\system32>Perl -MData::Dump=pp -e "pp do{()} "
()

    [download]

    Cheers Rolf
    (addicted to the Perl Programming Language :)
    Wikisyntax for the Monastery FootballPerl is like chess, only without the dice

[reply]
[d/l]
[select]
      Thanks, now I understand the difference: in the first case '()' wanted in scalar context which was forced by 'if' (so it becomes an undefined value).

      Added:
      An 'if' forces scalar context as 'and' do, so it may be that these two are internally implemented the same.
[reply]

In Section Seekers of Perl Wisdom

Log In?
Username:
Password:

What's my password?
Create A New User
Domain Nodelet?

www.com | www.net | www.org
Node Status?
node history
Node Type: note [id://11110538]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? • Last hour • Other CB clients
Other Users?
Others imbibing at the Monastery: (3)
As of 2024-04-24 19:00 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    No recent polls found