Well, this way would work... but there are others. Such as: 
my $total = scalar(keys %class1) + scalar(keys %class2) + scalar(keys 
+%class3);

#or

my $totb = 0;
$totb += $_ for map { scalar keys %$_; } (\%class1, \%class2, \%class3
+);

[download]
As for merging, I believe the answer to be no. A hash can not have two keys of the exact same value. You can create a union of them easily enough by using 
my %new = (%class1, %class2, %class3);

[download]
You will however lose any duplicates.

In reply to Re: Combining hashes by Sifmole
in thread Combining hashes by mpolo

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