how to check if a hash reference is empty in perl

Question

I need to test, whether my hashref contains 0 elements. I used this code: ``` $self = { fld => 1 }; %h = ( "a" => "b" ); $self->{href} = { %h }; print STDERR $self->{href}{ "a" }; print STDERR "
"; print "size of hash: " . keys( %h ) . ".
"; print "size of hashref: " . keys( $self->{href} ) . ".
"; ``` It works well with perl 5.16, but fails with perl 5.10: ``` Type of arg 1 to keys must be hash (not hash element) at - line 7, near "} ) " Execution of - aborted due to compilation errors. ```

Accepted Answer

If you'd use

```
%hash
```

for a hash, you'd use

```
%{ $hash }
```

for a reference, so it's

```
keys %{ $self->{href} }
```

Note: In some versions of Perl, `keys` accepts a reference. However, this was an experimental feature that was abandoned. One shouldn't use it.

how to check if a hash reference is empty in perl

Solution

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