in reply to Re^2: Why doesn't Perl provide %_ as the hash equivalent of @_ in subs?
in thread Why doesn't Perl provide %_ as the hash equivalent of @_ in subs?

"or will it be a reference (and how would that work)?"

I don't know enough about how Perl implements arrays and hashes and about how tied hashes work, to answer that.

But even if there's no good way to meaningfully allow modification of %_, that doesn't mean the magic variable should not be provided at all, it just means it should be read-only.

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Re^4: Why doesn't Perl provide %_ as the hash equivalent of @_ in subs?
by ikegami (Patriarch) on Sep 26, 2013 at 14:16 UTC
    It's possible to alias hash values. 
    $ perl -MData::Alias -E'
   @_ = ( a=>4 );
   alias %_ = @_;
   $_[1]=5; say $_{a};
   $_{a}=6; say $_[1];
'
5
6

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    However, copying args is a good thing. That's why we don't access @_ directly.

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Re^4: Why doesn't Perl provide %_ as the hash equivalent of @_ in subs?
by vsespb (Chaplain) on Sep 26, 2013 at 11:45 UTC
    that doesn't mean the magic variable should not be provided at all, it just means it should be read-only.
    That looks like inconsistency to me.
    sub f1
{
my ($x, $y) = @_;
z($x, $y);
}

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    and 
    sub f2
{
z($_[0], $_[1]);
}

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    Above two examples are not identical. Later one is something low-level, and it's just asking for trouble (for example in cases like f2($1), f2($.) or f2($x, $x) when z() modifies arguments ).
    (NOTE: another common point of view is that caller of such functions is asking for trouble)

    Example: 
    sub z
{
$_[0]++;
print $_[1]
}
sub f1
{
my ($x, $y) = @_;
z($x, $y);
}
my $x = 4;
f1($x, $x);

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    prints 4 
    sub z
{
$_[0]++;
print $_[1]
}
sub f2
{
z($_[0], $_[1]);
}
my $x = 4;
f2($x, $x);

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    prints 5

    So IMHO you should not use @_ just because it's shortest. Use it when you know what you're doing.

    And now you suggest add another %_ which behaves completely different way.

    Also making %_ readonly won't help much in cases when you pass magic variable as argument (example: RT#54728).
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