Re^2: if defined not working

Hi Athanasius,

I'm curious, what in your view is the advantage of using Logical Defined-Or over simple Logical Or in the OP's situation?

$ perl -Mstrict -Mwarnings -E'
my $foo;
say (defined $foo ? "1: defined" : "1: not defined");
my $bar = $foo;
say "2: bar: $bar";
my $baz = $foo || "baz";
say "3: baz: $baz";
my $qux = $foo // "qux";
say "4: qux: $qux";
'
1: not defined
Use of uninitialized value $bar in concatenation (.) or string at -e l
+ine 5.
2: bar: 
3: baz: baz
4: qux: qux
[download]

Thanks!

The way forward always starts with a minimal test.

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Re^3: if defined not working by stevieb (Canon) on Feb 04, 2016 at 17:01 UTC
Hey Nick, The difference really only matters if what you're checking has a false value (that you may not know about, such as when looping through a hash). A false value is still defined: `perl -wMstrict -E 'my $x=0; say $x\|\|1; say $x//2;' 1 0` [download] Update: here's a tiny example that shows that in a larger application, not checking for defined can be an issue when you aren't explicitly looking for truth: `use warnings; use strict; this(arg => 0); sub this { my %args = @_; do_something("if\n") if $args{arg}; do_something("if def\n") if defined $args{arg}; } sub do_something{ print shift; }` [download]	[reply] [d/l] [select]
Re^3: if defined not working by mr_mischief (Monsignor) on Feb 04, 2016 at 17:38 UTC
my $one = 1; my $zero = 0; my $undef; my $result; $result = 1; # 1 $result = 1 \|\| 0; # also 1 $result = 0 \|\| 1; # also 1 $result = $zero \|\| $one; # also 1 $result = $zero // $one; # 0 $result = $zero // 1; # 0 as well $result = 0 // 1; # 0 as well $result = $undef // $one; # 1 again $result = $undef \|\| $one; # 1 again $result = fork \|\| die; # dies in the child process or if failing to + fork $result = fork && die; # dies in the parent process $result = fork // die; # dies in process unable to fork a child # (beware the return values of function calls, for they are subtle and + quick to bite your behind) [download]	[reply] [d/l]