Re^2: Missing something with regards to references

Thank you for the explination.

It sort of make sense to me, but this is entirely new territory for me. I'd had a hunch at one time that the undef keys beneath the one I wanted would be a problem, but I couldn't quite wrap myself around what could be done about it. Using the reference rather than copies of values sort of makes sense too, but I think it needs time to sink in. I think the part about using $_[0] instead of shift makes the least sense to me... since I am always pathing through a reference, I apparently need to make a reference to the reference?

Anyway, thank you. This is very helpful.

Comment on Re^2: Missing something with regards to references

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Re^3: Missing something with regards to references by iblech (Friar) on Nov 03, 2004 at 10:47 UTC
since I am always pathing through a reference, I apparently need to make a reference to the reference? `\$_[0]` is not needed if the given (first) key is already a hashref. E.g.: `my %DATA = (3 => {}); put_element($DATA{3}, ...);` [download] But it is needed if the key doesn't exist yet: `my %DATA = (3 => {}); put_element($DATA{42}, ...);` [download] "But why doesn't `my $current = \shift` work? Why do I have to use `my $current = \$_[0]`?" Answer: If the key already exists and its value is a hashref, both possibilities work. But if the key does not exist, we have to make sure, that we really get a reference to the entry of `%DATA`, not the value of the non-existing entry. `sub test1 { my $val = shift; $val = 5; } sub test2 { $_[0] = 5; } my ($a, $b) = (3, 3); test1($a); # $a continues to be 3. test2($b); # $b is 5 now.` [download] But I could have missed something, too.	[reply] [d/l] [select]

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Re^3: Missing something with regards to references
by iblech (Friar) on Nov 03, 2004 at 10:47 UTC

since I am always pathing through a reference, I apparently need to make a reference to the reference?

\$_[0] is not needed if the given (first) key is already a hashref. E.g.:

my %DATA = (3 => {});

put_element($DATA{3}, ...);
[download]

But it is needed if the key doesn't exist yet:

my %DATA = (3 => {});

put_element($DATA{42}, ...);
[download]

"But why doesn't my $current = \shift work? Why do I have to use my $current = \$_[0]?" Answer: If the key already exists and its value is a hashref, both possibilities work. But if the key does not exist, we have to make sure, that we really get a reference to the entry of %DATA, not the value of the non-existing entry.

sub test1 {
  my $val = shift;
  $val = 5;
}

sub test2 {
  $_[0] = 5;
}

my ($a, $b) = (3, 3);

test1($a); # $a continues to be 3.
test2($b); # $b is 5 now.
[download]

But I could have missed something, too.

[reply]
[d/l]
[select]