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10.5. Passing Arrays and Hashes by Reference
10.5.1. Problem
You want to pass a function more
than one array or hash and have each remain distinct. For example,
you want to put the algorithm from Recipe 4.8 into a subroutine. This subroutine must then
be called with two arrays that remain distinct.
10.5.2. Solution
Pass arrays and hashes by reference, using the backslash
operator:
array_diff( \@array1, \@array2 );
10.5.3. Discussion
See Chapter 11 for more about manipulation of
references. Here's a subroutine that expects array references, along
with code to call it correctly:
@a = (1, 2);
@b = (5, 8);
@c = add_vecpair( \@a, \@b );
print "@c\n";
6 10
sub add_vecpair { # assumes both vectors the same length
my ($x, $y) = @_; # copy in the array references
my @result;
for (my $i=0; $i < @$x; $i++) {
$result[$i] = $x->[$i] + $y->[$i];
}
return @result;
}
A potential problem with this function is that it doesn't verify the
number and types of arguments passed into it. You could check
explicitly this way:
unless (@_ = = 2 && ref($x) eq 'ARRAY' && ref($y) eq 'ARRAY') {
die "usage: add_vecpair ARRAYREF1 ARRAYREF2";
}If all you plan to do is die on error (see Recipe 10.12), you can sometimes omit this check,
since dereferencing the wrong kind of reference triggers an exception
anyway. However, good defensive programming style encourages argument
validation for all functions.
10.5.4. See Also
The sections on "Passing References" and on "Prototypes" in Chapter 6
of Programming Perl and on "Pass by Reference"
in perlsub(1); Recipe 10.11; Chapter 11; Chapter 8 of
Programming Perl
