From: Dave Rolsky Date: Fri, 19 Jun 2009 15:49:14 +0000 (-0500) Subject: Finished slides for advanced attributes section. X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=5d57268450de0579773e5835629b68666fc4eb70;p=gitmo%2Fmoose-presentations.git Finished slides for advanced attributes section. Some tweaks for earlier slides. --- diff --git a/moose-class/slides/index.html b/moose-class/slides/index.html index 2ddbdc1..2acaf6c 100644 --- a/moose-class/slides/index.html +++ b/moose-class/slides/index.html @@ -884,14 +884,14 @@ use Moose;
  • Each call to extends resets your parents
    • -

    WRONG

    +

    Wrong

    package EvilEmployee;
 use Moose;
 extends 'Person';
 extends 'Thief';
    -

    RIGHT

    +

    Right

    package EvilEmployee;
 use Moose;
@@ -2363,6 +2363,50 @@ extends 'Report';
 
 
 
    
+  
    Method Modifiers Summary
    
+
+  
      
+    
    • Use before and after for ...
+      
        
+        
      • logging
        • 
+        
      • pre- or post-validation
        • 
+        
      • to add behavior to generated methods
        • 
+      
      
+    
      • 
+    
    • These two modifiers cannot change parameters or return values
      • 
+  
    
+
    
+
+
    
+  
    Method Modifiers Summary
    
+
+  
      
+    
    • Use around to ...
+      
        
+        
      • alter parameters passed to the original method
        • 
+        
      • alter the return value of the original method
        • 
+        
      • not call the original method at all (or call a different method)
        • 
+      
      
+    
      • 
+  
    
+
    
+
+
    
+  
    Method Modifiers Summary
    
+
+  
      
+    
    • When using modifiers in a role, require the modified method
      • 
+    
    • Use augment and inner to invert the normal subclassing flow ...
+      
        
+        
      • Least- to most-specific (parents to children)
        • 
+        
      • Build in "insertability" (stick more stuff in the "middle")
        • 
+      
      
+    
      • 
+    
    • Always call inner in the most specific subclass to allow for future extension
      • 
+  
    
+
    
+
+
    
   
    Questions?
    
 
      
 
@@ -2375,6 +2419,356 @@ extends 'Report';
 Iterate til this passes all its tests
    +
    +

    Part 5: Types

    +
    + +
    +

    Part 6: Advanced Attributes

    +
    + +
    +

    Weak References

    + +
      +
    • A weak reference lets you avoid circular references
      • +
    • Weak references do not increase the reference count
      • +
    +
    + +
    +

    Circular Reference Illustrated

    + + 
    my $foo = {};
+my $bar = { foo => $foo };
+$foo->{bar} = $bar;
    + +
      +
    • Neither $foo nor $bar go out of scope
      + (until the program exits)
      • +
    +
    + +
    +

    Weakening Circular References

    + + 
    use Scalar::Util qw( weaken );
+
+my $foo = {};
+my $bar = { foo => $foo };
+$foo->{bar} = $bar;
+weaken $foo->{bar}
    + +
      +
    • When $bar goes out of scope, $foo->{bar} becomes undef
      • +
    +
    + +
    +

    Circular References in Attributes

    + + 
    package Person;
+use Moose;
+
+has name   => ( is => 'ro' );
+has friend => ( is => 'rw' );
+
+my $alice = Person->new( name => 'Alice' );
+my $bob   = Person->new( name => 'Bob' );
+$bob->friend($alice);
+$alice->friend($bob);
    +
    + +
    +

    The Fix

    + + 
    package Person;
+use Moose;
+
+has name   => ( is => 'ro' );
+has friend => ( is => 'rw', weak_ref => 1 );
+
+my $alice = Person->new( name => 'Alice' );
+my $bob   = Person->new( name => 'Bob' );
+$bob->friend($alice);
+$alice->friend($bob);
    +
    + +
    +

    Under the Hood

    + +
      +
    • A weak_ref attribute calls weaken ... +
        +
      • during object construction
        • +
      • when the attribute is set via a writer
        • +
      +
      • +
    +
    + +
    +

    Triggers

    + +
      +
    • A code reference run after an attribute is set
      • +
    • Like an after modifier, but makes intentions clearer
      • +
    + +

    Gross

    + + 
    after salary_level => {
+    my $self = shift;
+    return unless @_;
+    $self->clear_salary;
+};
    +
    + +
    +

    Use a Trigger Instead

    + +

    Cleaner

    + + 
    has salary_level => (
+    is      => 'rw',
+    trigger => sub { $_[0]->clear_salary },
+);
    +
    + +
    +

    Delegation

    + +
      +
    • Attributes can be objects
      • +
    • Delegation transparently calls methods on those objects
      • +
    +
    + +
    +

    Delegation Examples

    + + 
    package Person;
+
+has lungs => (
+    is      => 'ro',
+    isa     => 'Lungs',
+    handles => [ 'inhale', 'exhale' ],
+);
    + +
      +
    • Creates $person->inhale and ->exhale methods
      • +
    • Internally calls $person->lungs->inhale
      • +
    +
    + +
    +

    Why Delegation?

    + +
      +
    • Reduce the number of classes exposed
      • +
    • Re-arrange class internals -
      + turn a method into an attribute with delegation
      • +
    • Provide convenenience methods
      • +
    +
    + +
    +

    Moose's handles Parameter

    + +
      +
    • Accepts many arguments ... +
        +
      • Array reference - list of methods to delegate as-is
        • +
      • Hash reference - map of method names
        • +
      • Regex - delegates all matching methods
        • +
      • Role name - delegates all methods in the role
        • +
      • Sub reference - does something complicated ;)
        • +
      +
      • +
    +
    + +
    +

    Array Reference

    + +
      +
    • Takes each method name and creates a simple delegation from the delegating class to the delegatee attribute
      • +
    +
    + +
    +

    Hash Reference

    + +
      +
    • Mapping of names in the delegating class to the delegatee class
      • +
    + + 
    package Person;
+use Moose;
+
+has account => (
+    is      => 'ro',
+    isa     => 'BankAccount',
+    handles => {
+        receive_money => 'deposit',
+        give_money    => 'withdraw',
+    },
+);
    +
    + +
    +

    Hash Reference Detailed

    + + 
        handles => {
+        receive_money => 'deposit',
+        give_money    => 'withdraw',
+    },
    + +
      +
    • $person->receive_money = $person->account->deposit
      • +
    • $person->give_money = $person->account->withdraw
      • +
    +
    + +
    +

    Regex

    + + 
    package Person;
+use Moose;
+
+has name => (
+    is      => 'ro',
+    isa     => 'Name',
+    handles => qr/.*/,
+);
    + +
      +
    • Creates a delegation for every method in the Name class
      • +
    • Excludes meta and methods inherited from Moose::Object
      • +
    +
    + +
    +

    Role Name

    + + 
    package Auditor;
+use Moose::Role;
+
+sub record_change  { ... }
+sub change_history { ... }
+
+package Account;
+use Moose;
+
+has history => (
+    is      => 'ro',
+    does    => 'Auditor',
+    handles => 'Auditor',
+);
    +
    + +
    +

    Role Name Detailed

    + +
      +
    • Account gets delegate methods for each method in the Auditor role +
        +
      • record_history
        • +
      • change_history
        • +
      +
      • +
    +
    + +
    +

    Traits and Metaclasses

    + +
      +
    • The ultimate in customization
      • +
    • Per attribute metaclasses
      • +
    • Per attribute roles applied to the attribute metaclass
      • +
    • Change the meta-level behavior
      • +
    +
    + +
    +

    Traits and Metaclasses

    + +
      +
    • The default metaclass is Moose::Meta::Attribute
      • +
    • Controls accessor generation, defaults, delegation, etc.
      • +
    • Adding a role to this metaclass (or replacing it) allows for infinite customization
      • +
    +
    + +
    +

    Traits and Metaclasses

    + +
      +
    • Can add/alter/remove attribute parameter (from has)
      • +
    • Can change behavior of created attribute
      • +
    +
    + +
    +

    Simple Trait Example

    + + 
    package Person;
+use Moose;
+use MooseX::LabeledAttributes;
+
+has ssn => (
+    traits => [ 'Labeled' ],
+    is     => 'ro',
+    isa    => 'Str',
+    label  => 'Social Security Number',
+);
+
+print Person->meta
+            ->get_attribute('ssn')->label;
    +
    + +
    +

    Simple Metaclass Example

    + + 
    package Person;
+use Moose;
+use MooseX::LabeledAttributes;
+
+has ssn => (
+    metaclass =>
+        'MooseX::Meta::Attribute::Labeled',
+    is        => 'ro',
+    isa       => 'Str',
+    label     => 'Social Security Number',
+);
+
+print Person->meta
+            ->get_attribute('ssn')->label;
    +
    + +
    +

    Traits vs Metaclass

    + +
      +
    • Can apply any mix of traits to an attribute
      • +
    • But just one metaclass
      • +
    • Traits (aka roles) can cooperate
      • +
    • Metaclasses require you to pick just one
      • +
    +
    + +
    +

    Advanced Attributes Summary

    + +
      +
    • Use weak_ref to avoid circular references
      • +
    • Use trigger to do an action post-attribute write
      • +
    • Use delegations to hide "internal" objects
      • +
    • Traits and metaclasses let you extend Moose's core attribute features
      • +
    +
    + diff --git a/moose-class/slides/ui/custom.css b/moose-class/slides/ui/custom.css index 1ae314f..0651329 100644 --- a/moose-class/slides/ui/custom.css +++ b/moose-class/slides/ui/custom.css @@ -76,6 +76,10 @@ img.for-slide { font-size: 33%; } +.slide pre.medium { + font-size: 80%; +} + .slide table.side-by-side tr { vertical-align: top; }