bless(\{hash => \{}}, $class);

That blesses a reference to a reference to a hash that contains a single value that is a reference to a reference of a hash.

The { } hashref construct creates a hash reference for you, so there is no need to put a backslash in front of it. That will only create a reference to the newly created reference to an anonymous hash.

Without the backslashes: 

bless { hash => {} }, $class;
...
$object->{hash}->{key_inside_that};

[download]
The arrow between two sets of braces is optional, and it's not the only notation. Here are a few alternatives (less good, imho): 
$object->{hash}{key_inside_that},
$$object{hash}{key_inside_that},
${${$object}{hash}}{key_inside_that}

[download]
If you don't remove the backslashes, you will have scalar references, and those can only be dereferenced with the ugly syntax: 
bless \{ hash => \{} }, $class;
...
${$$object->{hash}}->{key_inside_that};
${${${$object}}{hash}}{key_inside_that};
# etcetera...

[download]
Read perlref for more information.

HTH 

- Yes, I reinvent wheels.
- Spam: Visit eurotraQ.

In reply to Re: In a dereference nightmare! by Juerd
in thread In a dereference nightmare! by dargosch

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.