Mastering Modern Perl: Writing Efficient and Maintainable Code/

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Types of References I

Types of References I

Learn about the scalar, array, and hash references.

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Scalar references

The reference operator is the backslash \. In scalar context, it creates a single reference that refers to another value. In list context, it creates a list of references. To take a reference to $name, we can do this:

my $name = 'Larry';
my $name_ref = \$name;

We must dereference a reference to evaluate the value to which it refers. Dereferencing requires us to add an extra sigil for each level of dereferencing:

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sub reverse_in_place {
    my $name_ref = shift;
    $$name_ref = reverse $$name_ref;
}
my $name = 'Blabby';
reverse_in_place( \$name );
say $name;

The double scalar sigil $$ dereferences a scalar reference.

Parameters in @_ behave as aliasesThat is, if we access @_ directly, we can modify the arguments passed to the function. to caller variables so that we can modify them in place:

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sub reverse_value_in_place {
    $_[0] = reverse $_[0];
}
my $name = 'allizocohC';
reverse_value_in_place($name);
say $name;

We usually don’t want to modify values this way—callers rarely expect it, for example. Assigning parameters to lexicals within our functions makes copies of the values in @_ and avoids this aliasing behavior.

Note: Modifying a value in place or returning a reference to a scalar can save memory. Because Perl ...