Swap $key and $index parameters in ChoiceType

I've noticed the second parameter in the callback function for the options in the ChoiceType represents the index and the third the key. This patch brings the documentation in line with the code.
symfony · technetium · Jan 30, 2018 · Jan 30, 2018 · Jan 30, 2018 · a26069483ae3b0e4a3e6c3cdf7dcc122c804410b
commit a26069483ae3b0e4a3e6c3cdf7dcc122c804410b
diff --git a/reference/forms/types/choice.rst b/reference/forms/types/choice.rst
@@ -92,18 +92,18 @@ method::
             new Category('Cat3'),
             new Category('Cat4'),
         ],
-        'choice_label' => function($category, $key, $index) {
+        'choice_label' => function($category, $index, $key) {
             /** @var Category $category */
             return strtoupper($category->getName());
         },
-        'choice_attr' => function($category, $key, $index) {
+        'choice_attr' => function($category, $index, $key) {
             return ['class' => 'category_'.strtolower($category->getName())];
         },
-        'group_by' => function($category, $key, $index) {
+        'group_by' => function($category, $index, $key) {
             // randomly assign things into 2 groups
             return rand(0, 1) == 1 ? 'Group A' : 'Group B';
         },
-        'preferred_choices' => function($category, $key, $index) {
+        'preferred_choices' => function($category, $index, $key) {
             return $category->getName() == 'Cat2' || $category->getName() == 'Cat3';
         },
     ]);

diff --git a/reference/forms/types/options/choice_attr.rst.inc b/reference/forms/types/options/choice_attr.rst.inc
@@ -18,7 +18,7 @@ If an array, the keys of the ``choices`` array must be used as keys::
             'No' => false,
             'Maybe' => null,
         ),
-        'choice_attr' => function($val, $key, $index) {
+        'choice_attr' => function($val, $index, $key) {
             // adds a class like attending_yes, attending_no, etc
             return ['class' => 'attending_'.strtolower($key)];
         },

diff --git a/reference/forms/types/options/choice_label.rst.inc b/reference/forms/types/options/choice_label.rst.inc
@@ -16,7 +16,7 @@ more control::
             'no' => false,
             'maybe' => null,
         ),
-        'choice_label' => function ($value, $key, $index) {
+        'choice_label' => function ($value, $index, $key) {
             if ($value == true) {
                 return 'Definitely!';
             }

diff --git a/reference/forms/types/options/group_by.rst.inc b/reference/forms/types/options/group_by.rst.inc
@@ -22,7 +22,7 @@ Take the following example::
             '1 week' => new \DateTime('+1 week'),
             '1 month' => new \DateTime('+1 month')
         ),
-        'group_by' => function($val, $key, $index) {
+        'group_by' => function($val, $index, $key) {
             if ($val <= new \DateTime('+3 days')) {
                 return 'Soon';
             } else {