Yes, exactly!

After some thought, I need better (or just more) terminology.

Let us say that you use the \ and -> operators with "Perl references". Then let us say that Perl itself makes heavy use of a type of reference internally but we'll call these internal references "pointers" since that is probably less confusing for this discussion. Now a "pointer" isn't what a C programmer would call a pointer since there is at least one more layer of abstraction that isn't important for this discussion (so a "pointer" contains a C pointer plus a few other things).

So a Perl scalar variable is really a name for a "pointer" to a scalar value (called an SV in the source code). So $x points to some SV structure that contains $x's flags saying what type(s) of value(s) $x currently has and contains those values.

And a Perl array is an array of "pointers" to SVs. So calling test(@v) copies the "pointers" from @v to @_ so we end up with $v[0] and $_[0] pointing to the same SV structure and changing a value via one also changes the value seen via the other. The two are said to be aliases of each other.

But doing @_= @v causes new SV structs to be allocated for @_ and the values from @v's SVs are copied to @_'s new SVs.

And so doing "print $x" involves an "automatic dereference" of $x's "pointer".

Now a "Perl reference" is a(n) SV that contains a "pointer".

You can watch aliases in work via: 

sub refd {
    print join( " ", \(@_) ), $/;
}
my @v= qw( a b c );
print "@v: ", join( " ", \(@v) ), $/;
refd( @v );
refd( $v[0] );
refd( @v[1,2,0] );
refd( "$v[1]" );

[download]
You'll note that you get the same references except in the last case.

        - tye (but my friends call me "Tye")

In reply to (tye)Re2: Calling subroutine in a package from other perl sub. by tye
in thread Calling subroutine in a package from other perl sub. by Anonymous Monk

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