在Perl类中定义2D数组

Question

I am new to Perl and I am trying to define a 2D array as an attribute of my class in Perl. I define my class as follows,

sub new{
my $class = shift;
my $self = {};

my @board = [];
for (my $i = 0; $i < 8; $i++){
    for(my $j = 0; $j < 8; $j++){
        $board[$i][$j] = '.';
    }
}
$self->{board} = @board;
bless($self, $class);
return $self;
}

But later on when I try to access the board field like this

$self->{board}[$i][$j] = ' ';

I got an error saying

Can't use string ("8") as an ARRAY ref while "strict refs" in use

Can anyone tell me what is the correct way of doing this? I do not want to just delete use strict.

Answer 1

I changed your code to what I'm sure was your intention, see the lines changed and comment # not

sub new{
my $class = shift;
my $self = {};

my @board = ();  # not []
for (my $i = 0; $i < 8; $i++){
    for(my $j = 0; $j < 8; $j++){
        $board[$i][$j] = '.';
    }
}
$self->{board} = \@board; # not @board
bless($self, $class);
return $self;
}

or

sub new{
my $class = shift;
my $self = {};

my $board = []; # not @board
for (my $i = 0; $i < 8; $i++){
    for(my $j = 0; $j < 8; $j++){
        $board->[$i][$j] = '.';
    }
}
$self->{board} = $board; # not @board
bless($self, $class);
return $self;
}

about your my @board=[]; is the same as =([],); assign a list (that perl calls ARRAY) whose first element is a reference to an ARRAY to @board, but this is neither what make your code fail because you overwrite this empty array reference allocation and assignment to position zero. The @board is a list not a reference to it as $self->{board} expect

Answer 2

You need to place a reference to array inside your $self hash. Right now you're placing a value of array in scalar context - which is its length 8 . Of course you can't later use this as a reference to anything.

$self->{board} = \@board;

Answer 3

Others have given you explanations of what the problem is with your constructor. I'll add, that you can simplify it a bit by omitting the $board variable and using C-style loops.

sub new {
  my $class = shift;

  my $self = {};
  $self->{board} = [];

  for my $i (1 .. 8) {
    for my $j (1 .. 8) {
      $self->{board}[$i][$j] = '.';
    }
  }

  return bless $self, $class;
}

I'd also add the following three methods which make it easier to set and get the elements of the board:

sub board {
  my $self = shift;
  return $self->{board};
}

sub set_board_element {
  my $self = shift;
  my ($i, $j, $val) = @_;

  $self->board->[$i][$j] = $val;
}

sub get_board_element {
  my $self = shift;
  my ($i, $j) = @_;

  return $self->board->[$i][$j];
}

Have you considered using Moose to write your class? It will make your life easier. In particular, Array traits seem like a good fit for your problem.