在Perl中解引用数组

Question

Consider:

sub binary_search {
   my ($array, $word) = @_;
   my ($low, $high) = (0, @$array -1);
}

I am going through a book and the explanation for @$array the book provides is that it is dereferencing the scalar variable $array to get the array underneath.

I am a bit confused on this statement. I understand that $ is a scalar variable and @ is an array variable in Perl.

1. Why isn't it my (@array, $word) = @_; ?
2. How is there an array in $array (isn't $ a scalar?) which can be reached by @$array ?

Answer 1

The function expects a reference to an array, not an array, as the first argument. See perlreftut for info on array references. If you tried to evaluate:

my (@array, $word) = @_;

the @array would gobble up all the input and $word would be left undefined.

The method could have been written to expect a word and then an array, in which case you could do:

my ($word, @array) = @_;

but that's not what you have.

Note that when you call a function with an array in the actual argument list, what Perl does is interpolate the elements of the array as if they were individual arguments to the function. It does not pass the array as a single object. See the perlsub documentation for details.