In my moo-based class, building this attribute works fine:

has +dbh => (
    is => 'lazy',

    # must return only a code ref
    builder => sub {
        DBI->connect( "dbi:CSV:", undef, undef, {
                RaiseError => 1,
                PrintError => 1,
                f_ext      => ".csv/r",

                # Better performance with XS
                csv_class => "Text::CSV_XS",

                # csv_null => 1,
        } ) or die "Cannot connect: $DBI::errstr";
      }
);

[download]
When dumped, as expected it returns: $VAR1 = bless( {}, 'DBI::db' );

But, this code returns just a string instead of a file handle, which fails when I try to performs ops on it:

has base_file => (
    is       => 'rw',
    required => 1,

    #allow external names to be different from class attribute
    init_arg => 'base',
    builder  => sub {
        my $base_fh = IO::File->new( $_[0], '<' ) or die "$_[0]: $!";
        $base_fh->binmode(":utf8");
        return $base_fh;
      }
);

[download]

This is what I get:

$VAR2 = '..\\t\\merge_into.csv';

which of course fails when wanting to pass it to Text::CSV_XS:

... Can't call method "getline" without a package or object reference

Is there some special case for handling file handles in Moo? I tried returning a ref to the filehandle instead, but no joy. It worked fine as a procedural script before I converted it into a class, so the strategy works.

In reply to Confusion with Moo's builder attribute and a file handle by mgatto

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