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Re: Generating accessors for complex structures inside the object

by snoopy (Deacon)
on Jan 12, 2008 at 00:38 UTC ( #662015=note: print w/ replies, xml ) Need Help??


in reply to Generating accessors and mutators for complex structures inside the object

Here's a base class for generating flattened accessors for nested hash structs:

package Class::StructAccessors; use warnings; use strict; use Scalar::Util qw/reftype/; sub mk_struct_accessors { my ($class, $struct, $path, $key_seen, $ref_seen) = @_; $path ||= []; $key_seen ||= {}; $ref_seen ||= {}; while (my ($k,$v) = each %$struct) { my $reftype = reftype($v)||''; if ($reftype) { die "Bad reference type: $reftype" unless ($reftype eq 'HASH'); die "Cycle detected at $v" if ($ref_seen->{$v}); $ref_seen->{$v} = 1; $class->mk_struct_accessors($v, [@$path, $k], $key_seen, $ +ref_seen); } else { die "null key" unless (defined $v && $v ne ''); die "Duplicate key detected $v" if ($key_seen->{$v}); $key_seen->{$v} = 1; # # add this accessor to the class # no strict 'refs'; warn "adding: $v"; *$v = sub { my $self = shift; return $self->_dereference(@$path, $k, $v); } } } } sub _dereference { my $self = shift; my @hash_keys = @_; my $ref = $self; while (@hash_keys && $ref) { $ref = $ref->{shift(@hash_keys)}; } return $ref; } 1;
It dies if the struct contains any duplicate keys or cycles.

A test script follows:

package Foo; use base qw{Class::StructAccessors}; __PACKAGE__->mk_struct_accessors({ A => { B => 'C' }, D => { E => { F => 'G' } }, ## Z => 'G', # Duplicate test ## X => [1,2,3], # Bad type test ## N => do {my $cycle = {}; $cycle->{M} = $cycle; $cycle;}, # Cyclic + test }); package main; use Foo; my $obj = bless { A => { B => {'C' => "It's hello from C"}, }, D => { E => { F => {'G' => "G'day from G"} } } }, 'Foo'; print "C:".$obj->C."\n"; print "G:".$obj->G."\n";

Update: Added test for cycles.


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Re^2: Generating accessors for complex structures inside the object
by KSURi (Monk) on Jan 12, 2008 at 14:55 UTC
    Thanks! I'll try your code asap. Unfortunately I can't do this now =(
Re^2: Generating accessors for complex structures inside the object
by KSURi (Monk) on Jan 14, 2008 at 21:31 UTC
    I've read your code attentively, now I want to ask a few questions please. Here:
    ... D => { E => { F => 'G' } }, ## Z => 'G', # Duplicate test ...
    If I'll uncomment 'Z' key there will be a warning thrown about duplicate 'G' key. But 'G' is not a key here, it's keys value.

    And here:
    ## X => [1,2,3], # Bad type test
    Why arrayref is a bad type?

    And the last one: I tried to add mutators to your code through assignment the lvalue attribute to _derefernce sub but it has no effect =( Any ideas of how can I do this?
      Hi KSURi,

      Thanks for your questions. Before getting into the details; I did make some assumptions that need to be tested:

      The class level structure (defined in Foo) is a effectively a struct definition:

      So, if in Foo, you define

      package Foo; use base qw/Class::StructAccessors/; __PACKAGE__->mk_struct_accessors({A => {B => C}});
      then the actual method created is C.

      my $obj = {}; bless $obj, "Foo"; $obj->{A}{B}{C} = "this is a C"; print $obj->C; # outputs "this is a C"
      If you want another object with another fixed structure, then you need another class
      package Bar; use base qw/Class::StructAccessors/; __PACKAGE__->mk_struct_accessors({X => {Y => Z}});
      This will generate accessor method for Z.

      In an nutshell, the above code works when you have finite number of structures that are know at run time.

      I'm getting the feeling that you want a more dynamic solution that'll work at the instance on any structure; something like:

      my $obj = bless {a => {b => {c => 'data for c'}}}, "Class::StructAc +cessorMk2";
      Always happy to assist (and code) :-) Please advise.
        > I'm getting the feeling that you want a more dynamic solution that'll work at the instance on any structure; Yep, that will be very usefull not only for me. Though I've solved my own problem (through object redesigning) I'll be glad to read ideas and etc. Thanks for your assist)

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