SplFixedArray can be used in nested 'foreach' loops

Because SplFixedArray is an Iterator, and stores its own iteration state, it cannot be
used in nested 'foreach' loops. If you try, the inner loop will overwrite the iteration
position of the outer loop, so that the outer loop 'thinks' it is finished after the inner
loop finishes.

To illustrate:

    $spl = SplFixedArray::fromArray([0, 1]);
    foreach ($spl as $a) {
      foreach ($spl as $b) {
        echo "$a $b";
      }
    }

Only prints two lines:

    0 0
    0 1

Interestingly, though SplFixedArray has methods like ::current(), ::next(), etc., these
are not used by the 'foreach' loop. Rather, an instance of '_spl_fixedarray_it' is created
internally and used to track the iteration state.

Therefore, if the current iteration position is stored in '_spl_fixedarray_it', the nested
'foreach' loops will not interfere with each other in this way.

However, the problem is that ::current(), ::next(), etc. are still part of the SplFixedArray
interface and users may expect them to 'work' in a 'foreach' loop. For ::next() and ::rewind(),
there is nothing we can do, since the SplFixedArray instance does not keep any reference to
the _spl_fixedarray_it structures being used by the 'foreach' loops. However, we can still keep
::valid(), ::current(), and ::key() working by keeping a current iteration position in each
SplFixedArray instance and updating it at the same time as we update the _spl_fixedarray_it.

Although, they still break in cases like this:

    foreach ($spl as $a) {
      foreach ($spl as $b) {
        // do something
      }
      $spl->key(); // will NOT return iteration position of outer loop
    }

Overall, this fix stinks and it may be better to bite the bullet and convert SplFixedArray
to IteratorAggregate.

Author: alexdowad

ext/spl/spl_fixedarray.c

@@ -52,7 +52,7 @@ typedef struct _spl_fixedarray_object { /* {{{ */
 	zend_function         *fptr_offset_has;
 	zend_function         *fptr_offset_del;
 	zend_function         *fptr_count;
-	int                    current;
+	int                    current; /* used by SplFixedArray::current(), ::next(), etc. */
 	int                    flags;
 	zend_class_entry      *ce_get_iterator;
 	zend_object            std;
@@ -61,6 +61,9 @@ typedef struct _spl_fixedarray_object { /* {{{ */
 
 typedef struct _spl_fixedarray_it { /* {{{ */
 	zend_user_iterator     intern;
+	/* _spl_fixedarray_it.current is used by iterator created via spl_fixedarray_get_iterator()
+	 * This makes nested 'foreach' loops work correctly */
+	int                    current;
 } spl_fixedarray_it;
 /* }}} */
 
@@ -806,25 +809,29 @@ static void spl_fixedarray_it_dtor(zend_object_iterator *iter) /* {{{ */
 
 static void spl_fixedarray_it_rewind(zend_object_iterator *iter) /* {{{ */
 {
-	spl_fixedarray_object *object = Z_SPLFIXEDARRAY_P(&iter->data);
+	spl_fixedarray_object *object   = Z_SPLFIXEDARRAY_P(&iter->data);
+	spl_fixedarray_it     *iterator = (spl_fixedarray_it *)iter;
 
 	if (object->flags & SPL_FIXEDARRAY_OVERLOADED_REWIND) {
 		zend_user_it_rewind(iter);
 	} else {
-		object->current = 0;
+		/* Update object->current so that if $array->key() is called in a 'foreach'
+		 * block, it will return the expected value */
+		object->current = iterator->current = 0;
 	}
 }
 /* }}} */
 
 static int spl_fixedarray_it_valid(zend_object_iterator *iter) /* {{{ */
 {
-	spl_fixedarray_object *object = Z_SPLFIXEDARRAY_P(&iter->data);
+	spl_fixedarray_object *object   = Z_SPLFIXEDARRAY_P(&iter->data);
+	spl_fixedarray_it     *iterator = (spl_fixedarray_it *)iter;
 
 	if (object->flags & SPL_FIXEDARRAY_OVERLOADED_VALID) {
 		return zend_user_it_valid(iter);
 	}
 
-	if (object->current >= 0 && object->current < object->array.size) {
+	if (iterator->current >= 0 && iterator->current < object->array.size) {
 		return SUCCESS;
 	}
 
@@ -835,14 +842,15 @@ static int spl_fixedarray_it_valid(zend_object_iterator *iter) /* {{{ */
 static zval *spl_fixedarray_it_get_current_data(zend_object_iterator *iter) /* {{{ */
 {
 	zval zindex;
-	spl_fixedarray_object *object = Z_SPLFIXEDARRAY_P(&iter->data);
+	spl_fixedarray_object *object   = Z_SPLFIXEDARRAY_P(&iter->data);
+	spl_fixedarray_it     *iterator = (spl_fixedarray_it *)iter;
 
 	if (object->flags & SPL_FIXEDARRAY_OVERLOADED_CURRENT) {
 		return zend_user_it_get_current_data(iter);
 	} else {
 		zval *data;
 
-		ZVAL_LONG(&zindex, object->current);
+		ZVAL_LONG(&zindex, iterator->current);
 
 		data = spl_fixedarray_object_read_dimension_helper(object, &zindex);
 
@@ -856,25 +864,29 @@ static zval *spl_fixedarray_it_get_current_data(zend_object_iterator *iter) /* {
 
 static void spl_fixedarray_it_get_current_key(zend_object_iterator *iter, zval *key) /* {{{ */
 {
-	spl_fixedarray_object *object = Z_SPLFIXEDARRAY_P(&iter->data);
+	spl_fixedarray_object *object   = Z_SPLFIXEDARRAY_P(&iter->data);
+	spl_fixedarray_it     *iterator = (spl_fixedarray_it *)iter;
 
 	if (object->flags & SPL_FIXEDARRAY_OVERLOADED_KEY) {
 		zend_user_it_get_current_key(iter, key);
 	} else {
-		ZVAL_LONG(key, object->current);
+		ZVAL_LONG(key, iterator->current);
 	}
 }
 /* }}} */
 
 static void spl_fixedarray_it_move_forward(zend_object_iterator *iter) /* {{{ */
 {
-	spl_fixedarray_object *object = Z_SPLFIXEDARRAY_P(&iter->data);
+	spl_fixedarray_object *object   = Z_SPLFIXEDARRAY_P(&iter->data);
+	spl_fixedarray_it     *iterator = (spl_fixedarray_it *)iter;
 
 	if (object->flags & SPL_FIXEDARRAY_OVERLOADED_NEXT) {
 		zend_user_it_move_forward(iter);
 	} else {
 		zend_user_it_invalidate_current(iter);
-		object->current++;
+		/* Update object->current so that if $array->key() is called in a 'foreach'
+		 * block, it will return the expected value */
+		object->current = ++iterator->current;
 	}
 }
 /* }}} */
@@ -986,6 +998,7 @@ zend_object_iterator *spl_fixedarray_get_iterator(zend_class_entry *ce, zval *ob
 	ZVAL_OBJ(&iterator->intern.it.data, Z_OBJ_P(object));
 	iterator->intern.it.funcs = &spl_fixedarray_it_funcs;
 	iterator->intern.ce = ce;
+	iterator->current = 0;
 	ZVAL_UNDEF(&iterator->intern.value);
 
 	return &iterator->intern.it;

ext/spl/tests/SplFixedArray_nested_foreach.phpt

@@ -0,0 +1,19 @@
+--TEST--
+Nested iteration of SplFixedArray using foreach loops
+--FILE--
+<?php
+
+$array = SplFixedArray::fromArray([0, 1]);
+
+foreach ($array as $value1) {
+  foreach ($array as $value2) {
+    echo "$value1 $value2\n";
+  }
+}
+
+?>
+--EXPECT--
+0 0
+0 1
+1 0
+1 1