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Re^2: Entering the land of Perl

by manbroski (Initiate)
on Apr 04, 2013 at 23:52 UTC ( #1027051=note: print w/ replies, xml ) Need Help??


in reply to Re: Entering the land of Perl
in thread Entering the land of Perl

Good call on the letters versus characters. But as far as the prototype passing, I was certain that it enforces a pass by reference. Notice that I have to dereference it after the passage. So the hope is that there is no copying.


Comment on Re^2: Entering the land of Perl
Re^3: Entering the land of Perl
by 2teez (Priest) on Apr 05, 2013 at 03:17 UTC

    Hi manbroski,

    "..Notice that I have to dereference it after the passage.." Why is that?

    Did you also notice your subroutine sort_and_print_hash_keys definition

    sub sort_and_print_hash_keys (\%) {..
    and how you eventually used the it like so:
    sort_and_print_hash_keys(%letters); # you passed a hash variable not a + hash ref.
    ".. But as far as the prototype passing, I was certain that it enforces a pass by reference..."

    If I may suggest, you will do well yielding the wisdom of jwkrahn, as regard the usage of prototype for this reason:

    When you use a reference prototype, like "\$", "\@", "\%" "...those symbols don't actually say that you must pass in a scalar reference, an array reference, and a hash reference. Rather, they say you must pass in a scalar variable, an array variable, and a hash variable. That means that the compiler insists upon seeing a properly notated variable of the given type, complete with "$", "@", or "%" in that slot. You must not use a backslash. The compiler silently supplies the backslash for you... "
    from Far More than Everything You've Ever Wanted to Know about Prototypes in Perl -- by Tom Christiansen
    -- by liverpole, under subheading Problems with Reference Prototypes

    Hope this helps.

    If you tell me, I'll forget.
    If you show me, I'll remember.
    if you involve me, I'll understand.
    --- Author unknown to me
Re^3: Entering the land of Perl
by jwkrahn (Monsignor) on Apr 05, 2013 at 14:37 UTC
    Notice that I have to dereference it after the passage. So the hope is that there is no copying.

    In your code you have:

    sub sort_and_print_hash_keys (\%) { my %hash = %{shift()}; foreach (sort keys %hash) { print "$hash{$_} "; } print "\n"; }

    Which is copying the entire hash.    If you didn't want to copy the hash you could do it like this:

    sub sort_and_print_hash_keys (\%) { my $hash = shift; foreach (sort keys %$hash) { print "$hash->{$_} "; } print "\n"; }

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