Re: my $x or my ($x)

[Melly]

in reply to my $x or my ($x)

AFAIK the list context just allows you to declare a whole bunch of vars in one go - e.g.

my $foo;
my $bar;

and

my ($foo, $bar);

are the same.

[jhourcle]

Although it's convenient that you can declare a whole lot of variables in one line, the big advantage is that you can handle assignments at the same time:

my ($foo, $bar) = @array;

The only warning I can give is that using an undef in the list will throw warnings (errors?) in older versions of perl:

my (undef, $foo, undef, $bar) = @array;

You can assign values from a list of scalars, as well, but I think it's less legible than assigning one at a time:

 my ($foo, $bar, $baz) = (27, 'blah', $x);

[ptum]

One common mistake that is made when assigning to a collection of scalars is this:

my ($one, $two, $three, $four) = 0;

People tend to think that all four variables are initialized, but really only $one is set to zero, the rest are still undef. You'd have to explicitly set each variable to achieve that result:

my $one = my $two = my $three = my $four = 0;

... or alternatively:

my ($one, $two, $three, $four) = (0,0,0,0);

But as was stated elsewhere, this lacks readability for large collections of scalars. In general, I tend to declare my variables and either initialize them to zero or leave them undefined, then assigning their values in later statements. I hate getting warnings about variables being undef when evaluating in a conditional statement.

[eff_i_g]

Just a quick addition to ptum's. I would write:

my ($one, $two, $three, $four) = (0,0,0,0);

as

my ($one, $two, $three, $four) = (0) x 4;

[Rhandom]

The only warning I can give is that using an undef in the list will throw warnings (errors?) in older versions of perl:
my (undef, $foo, undef, $bar) = @array;

Never fear. Just move your my.


(undef, my $foo, undef, my $bar) = @array;


This is particularly more useful in cases where you already have a declared variable.


my $foo = "ab";
(my $avar, $foo) = ($foo =~ /(.)(.)/);

[benizi]

I prefer slicing. Instead of:

my (undef, $foo, undef, $bar) = @array;

or

(undef, my $foo, undef, my $bar) = @array;

do:

my ($foo, $bar) = @array[1,3];

e.g.

my ($size, $mtime) = (stat $filename)[7,9];