What is the use de-referencing and creating a new anonymous hash in new() and rnew() ?

sathiya.sw has asked for the wisdom of the Perl Monks concerning the following question:

I have been going through the module Devel::Symdump.
There i have seen a line of code which i would want a better clarification.,

my $self = bless {%${"$class\::Defaults"}}, $class;
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It is a reference and dereferencing operation ? Am i right?? Or else some thing is also achieved here?
Why this is needed ? What is the intension in doing this ??

Sathiyamoorthy

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Re: What is the use de-referencing and creating a new anonymous hash in new() and rnew() ? by almut (Canon) on Nov 28, 2008 at 15:10 UTC
`${"$class\::Defaults"}` is a symbolic reference to the `Defaults` hash in the respective class (`Devel::Symdump` here). The `%` dereferences it, so the resulting hash's flattened content will initialise the anonymous hash `{...}` which is going to hold the instance data of the object that is created by blessing the hashref into `$class`.	[reply] [d/l] [select]
Re: What is the use de-referencing and creating a new anonymous hash in new() and rnew() ? by ysth (Canon) on Nov 28, 2008 at 16:52 UTC
This is a poor way of going about things. As noted, a subclass can have its own Defaults. The problem is that a subclass does not default to having the same defaults as its superclass. This would be better: `{ my %Defaults = ...; sub Defaults { \%Defaults } } sub new { my $class = shift; my $self = bless { %{ $class->Defaults } }, $class;` [download] -- Online Fortune Cookie Search Office Space merchandise	[reply] [d/l]
Re: What is the use de-referencing and creating a new anonymous hash in new() and rnew() ? by zwon (Abbot) on Nov 28, 2008 at 14:58 UTC
Symdump contains Defaults hash with default values for object. This code creates a copy of this hash and blesses it into class. Note that subclass can define its own Defaults and this still will work.	[reply]
Re: What is the use de-referencing and creating a new anonymous hash in new() and rnew() ? by pobocks (Chaplain) on Nov 29, 2008 at 10:15 UTC
Maybe I was the only one thick enough to have to take a minute to figure this out, but the '\' there is to prevent interpretation of '::' as the package directory separator, and enforce interpolation of '$class' instead of '$class::Defaults'. Again, you probably all knew that, or realized it from other comments... but it threw me for a 2-second loop. `for(split(" ","tsuJ rehtonA lreP rekcaH")){print reverse . " "}print "\b.\n";`	[reply] [d/l]