Merge pull request #430 from muffato/master

Add next-value buffering to Bio::EnsEMBL::Utils::Iterator

modules/Bio/EnsEMBL/Utils/Iterator.pm

@@ -141,6 +141,26 @@ sub new {
 }
 
 
+=head2 _fetch_next_value_if_needed
+
+  Example    : $iterator->_fetch_next_value_if_needed
+  Description: Helper method used to fill the internal buffer with the next value of the iterator
+  Returntype : none
+  Exceptions : none
+  Caller     : general
+  Status     : Experimental
+
+=cut
+
+sub _fetch_next_value_if_needed {
+    my $self = shift;
+
+    unless (exists $self->{next}) {
+        $self->{next} = $self->{sub}->();
+    }
+}
+
+
 =head2 next
 
   Example    : $obj = $iterator->next
@@ -155,9 +175,12 @@ sub new {
 sub next {
     my $self = shift;
 
-    $self->{next} = $self->{sub}->() unless defined $self->{next};
-    
-    return delete $self->{next};
+    $self->_fetch_next_value_if_needed();
+
+    if (defined $self->{next}) {
+        return delete $self->{next};
+    }
+    return;
 }
 
 =head2 has_next
@@ -175,7 +198,7 @@ sub next {
 sub has_next {
     my $self = shift;
 
-    $self->{next} = $self->{sub}->() unless defined $self->{next};
+    $self->_fetch_next_value_if_needed();
 
     return defined $self->{next}; 
 }
@@ -196,7 +219,7 @@ sub has_next {
 sub peek {
     my $self = shift;
 
-    $self->{next} = $self->{sub}->() unless defined $self->{next};
+    $self->_fetch_next_value_if_needed();
 
     return $self->{next};
 }

modules/t/iterator.t

@@ -33,6 +33,23 @@ $it = Bio::EnsEMBL::Utils::Iterator->new(sub {return 3});
 
 is($it->next, 3, "got expected value from iterator created from coderef");
 
+# check that the coderef is not called any more once it returns undef
+
+my $call_counter = 0;
+$it = Bio::EnsEMBL::Utils::Iterator->new(sub {
+        ++$call_counter;
+        if ($call_counter == 1) {
+            return 1;
+        } else {
+            return undef;
+        }
+    });
+
+is($it->next, 1, "got expected value from iterator created from coderef");
+is($it->next, undef, "got undef from iterator created from coderef once exhausted");
+is($it->next, undef, "got undef from iterator created from coderef once exhausted");
+is($call_counter, 2, 'Returned undef without calling the coderef any further');
+
 # from now on we create an iterator from an arrayref because it's simpler
 
 $it = Bio::EnsEMBL::Utils::Iterator->new([1,2,3]);