From: Dave Rolsky <autarch@urth.org>
Date: Thu, 24 Sep 2009 20:16:03 +0000 (-0500)
Subject: simplify history recording task
X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=648519ab804c5615378bc31788510ffbef319fe2;p=gitmo%2Fmoose-presentations.git

simplify history recording task
---

diff --git a/moose-class/exercises/answers/06-advanced-attributes/BankAccount.pm b/moose-class/exercises/answers/06-advanced-attributes/BankAccount.pm
index 5c0035b..90c78e2 100644
--- a/moose-class/exercises/answers/06-advanced-attributes/BankAccount.pm
+++ b/moose-class/exercises/answers/06-advanced-attributes/BankAccount.pm
@@ -7,7 +7,7 @@ has balance => (
     is      => 'rw',
     isa     => 'Int',
     default => 100,
-    trigger => sub { $_[0]->_record_difference( $_[1] ) },
+    trigger => sub { shift->_record_balance(@_) },
 );
 
 has owner => (
@@ -22,12 +22,6 @@ has history => (
     default => sub { [] },
 );
 
-sub BUILD {
-    my $self = shift;
-
-    $self->_record_difference( $self->balance );
-}
-
 sub deposit {
     my $self   = shift;
     my $amount = shift;
@@ -45,13 +39,12 @@ sub withdraw {
     $self->balance( $self->balance - $amount );
 }
 
-sub _record_difference {
-    my $self      = shift;
-    my $new_value = shift;
-
-    my $old_value = sum @{ $self->history };
+sub _record_balance {
+    my $self = shift;
+    shift;
+    my $old_value = shift;
 
-    push @{ $self->history }, $new_value - ( $old_value || 0 );
+    push @{ $self->history }, $old_value;
 }
 
 no Moose;
diff --git a/moose-class/exercises/t/06-advanced-attributes.t b/moose-class/exercises/t/06-advanced-attributes.t
index 138ef26..23ec690 100644
--- a/moose-class/exercises/t/06-advanced-attributes.t
+++ b/moose-class/exercises/t/06-advanced-attributes.t
@@ -13,11 +13,8 @@
 # Finally, add a read-only history attribute. This will be an ArrayRef
 # of Int's. This should default to an empty array reference.
 #
-# Use a trigger to record the _difference_ after each change to the
-# balance. The previous balance is the sum of all the previous
-# changes. You can use List::Util's sum function to calculate this. To
-# avoid warnings the first time history is recorded, default to 0 if
-# history is empty.
+# Use a trigger to record the _old value_ of the balance each time it
+# changes.
 #
 # Use a BUILD method in BankAccount to record the original balance in
 # the history.
diff --git a/moose-class/exercises/t/lib/MooseClass/Tests.pm b/moose-class/exercises/t/lib/MooseClass/Tests.pm
index eaa8a24..100758a 100644
--- a/moose-class/exercises/t/lib/MooseClass/Tests.pm
+++ b/moose-class/exercises/t/lib/MooseClass/Tests.pm
@@ -467,11 +467,15 @@ sub person06 {
         'owner of bank account is person that created account' );
 
     $person->deposit(10);
-    is_deeply( $person->account->history, [ 100, 10 ],
+    is_deeply( $person->account->history, [ 100 ],
                'deposit was recorded in account history' );
 
     $person->withdraw(15);
-    is_deeply( $person->account->history, [ 100, 10, -15 ],
+    is_deeply( $person->account->history, [ 100, 110 ],
+               'withdrawal was recorded in account history' );
+
+    $person->withdraw(45);
+    is_deeply( $person->account->history, [ 100, 110, 95 ],
                'withdrawal was recorded in account history' );
 }