bevy/crates/bevy_reflect/src/tuple.rs
Zachary Harrold bf765e61b5
Add no_std support to bevy_reflect (#16256)
# Objective

- Contributes to #15460

## Solution

- Added `std` feature (enabled by default)

## Testing

- CI
- `cargo check -p bevy_reflect --no-default-features --target
"x86_64-unknown-none"`
- UEFI demo application runs with this branch of `bevy_reflect`,
allowing `derive(Reflect)`

## Notes

- The [`spin`](https://crates.io/crates/spin) crate has been included to
provide `RwLock` and `Once` (as an alternative to `OnceLock`) when the
`std` feature is not enabled. Another alternative may be more desirable,
please provide feedback if you have a strong opinion here!
- Certain items (`Box`, `String`, `ToString`) provided by `alloc` have
been added to `__macro_exports` as a way to avoid `alloc` vs `std`
namespacing. I'm personally quite annoyed that we can't rely on `alloc`
as a crate name in `std` environments within macros. I'd love an
alternative to my approach here, but I suspect it's the least-bad
option.
- I would've liked to have an `alloc` feature (for allocation-free
`bevy_reflect`), unfortunately, `erased_serde` unconditionally requires
access to `Box`. Maybe one day we could design around this, but for now
it just means `bevy_reflect` requires `alloc`.

---------

Co-authored-by: Gino Valente <49806985+MrGVSV@users.noreply.github.com>
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2024-12-05 21:15:21 +00:00

816 lines
23 KiB
Rust

use bevy_reflect_derive::impl_type_path;
use variadics_please::all_tuples;
use crate::generics::impl_generic_info_methods;
use crate::{
self as bevy_reflect, type_info::impl_type_methods, utility::GenericTypePathCell, ApplyError,
FromReflect, Generics, GetTypeRegistration, MaybeTyped, PartialReflect, Reflect, ReflectKind,
ReflectMut, ReflectOwned, ReflectRef, Type, TypeInfo, TypePath, TypeRegistration, TypeRegistry,
Typed, UnnamedField,
};
use alloc::{boxed::Box, vec, vec::Vec};
use core::{
any::Any,
fmt::{Debug, Formatter},
slice::Iter,
};
/// A trait used to power [tuple-like] operations via [reflection].
///
/// This trait uses the [`Reflect`] trait to allow implementors to have their fields
/// be dynamically addressed by index.
///
/// This trait is automatically implemented for arbitrary tuples of up to 12
/// elements, provided that each element implements [`Reflect`].
///
/// # Example
///
/// ```
/// use bevy_reflect::{PartialReflect, Tuple};
///
/// let foo = (123_u32, true);
/// assert_eq!(foo.field_len(), 2);
///
/// let field: &dyn PartialReflect = foo.field(0).unwrap();
/// assert_eq!(field.try_downcast_ref::<u32>(), Some(&123));
/// ```
///
/// [tuple-like]: https://doc.rust-lang.org/book/ch03-02-data-types.html#the-tuple-type
/// [reflection]: crate
pub trait Tuple: PartialReflect {
/// Returns a reference to the value of the field with index `index` as a
/// `&dyn Reflect`.
fn field(&self, index: usize) -> Option<&dyn PartialReflect>;
/// Returns a mutable reference to the value of the field with index `index`
/// as a `&mut dyn Reflect`.
fn field_mut(&mut self, index: usize) -> Option<&mut dyn PartialReflect>;
/// Returns the number of fields in the tuple.
fn field_len(&self) -> usize;
/// Returns an iterator over the values of the tuple's fields.
fn iter_fields(&self) -> TupleFieldIter;
/// Drain the fields of this tuple to get a vector of owned values.
fn drain(self: Box<Self>) -> Vec<Box<dyn PartialReflect>>;
/// Clones the struct into a [`DynamicTuple`].
fn clone_dynamic(&self) -> DynamicTuple;
/// Will return `None` if [`TypeInfo`] is not available.
fn get_represented_tuple_info(&self) -> Option<&'static TupleInfo> {
self.get_represented_type_info()?.as_tuple().ok()
}
}
/// An iterator over the field values of a tuple.
pub struct TupleFieldIter<'a> {
pub(crate) tuple: &'a dyn Tuple,
pub(crate) index: usize,
}
impl<'a> TupleFieldIter<'a> {
pub fn new(value: &'a dyn Tuple) -> Self {
TupleFieldIter {
tuple: value,
index: 0,
}
}
}
impl<'a> Iterator for TupleFieldIter<'a> {
type Item = &'a dyn PartialReflect;
fn next(&mut self) -> Option<Self::Item> {
let value = self.tuple.field(self.index);
self.index += value.is_some() as usize;
value
}
fn size_hint(&self) -> (usize, Option<usize>) {
let size = self.tuple.field_len();
(size, Some(size))
}
}
impl<'a> ExactSizeIterator for TupleFieldIter<'a> {}
/// A convenience trait which combines fetching and downcasting of tuple
/// fields.
///
/// # Example
///
/// ```
/// use bevy_reflect::GetTupleField;
///
/// # fn main() {
/// let foo = ("blue".to_string(), 42_i32);
///
/// assert_eq!(foo.get_field::<String>(0), Some(&"blue".to_string()));
/// assert_eq!(foo.get_field::<i32>(1), Some(&42));
/// # }
/// ```
pub trait GetTupleField {
/// Returns a reference to the value of the field with index `index`,
/// downcast to `T`.
fn get_field<T: Reflect>(&self, index: usize) -> Option<&T>;
/// Returns a mutable reference to the value of the field with index
/// `index`, downcast to `T`.
fn get_field_mut<T: Reflect>(&mut self, index: usize) -> Option<&mut T>;
}
impl<S: Tuple> GetTupleField for S {
fn get_field<T: Reflect>(&self, index: usize) -> Option<&T> {
self.field(index)
.and_then(|value| value.try_downcast_ref::<T>())
}
fn get_field_mut<T: Reflect>(&mut self, index: usize) -> Option<&mut T> {
self.field_mut(index)
.and_then(|value| value.try_downcast_mut::<T>())
}
}
impl GetTupleField for dyn Tuple {
fn get_field<T: Reflect>(&self, index: usize) -> Option<&T> {
self.field(index)
.and_then(|value| value.try_downcast_ref::<T>())
}
fn get_field_mut<T: Reflect>(&mut self, index: usize) -> Option<&mut T> {
self.field_mut(index)
.and_then(|value| value.try_downcast_mut::<T>())
}
}
/// A container for compile-time tuple info.
#[derive(Clone, Debug)]
pub struct TupleInfo {
ty: Type,
generics: Generics,
fields: Box<[UnnamedField]>,
#[cfg(feature = "documentation")]
docs: Option<&'static str>,
}
impl TupleInfo {
/// Create a new [`TupleInfo`].
///
/// # Arguments
///
/// * `fields`: The fields of this tuple in the order they are defined
pub fn new<T: Reflect + TypePath>(fields: &[UnnamedField]) -> Self {
Self {
ty: Type::of::<T>(),
generics: Generics::new(),
fields: fields.to_vec().into_boxed_slice(),
#[cfg(feature = "documentation")]
docs: None,
}
}
/// Sets the docstring for this tuple.
#[cfg(feature = "documentation")]
pub fn with_docs(self, docs: Option<&'static str>) -> Self {
Self { docs, ..self }
}
/// Get the field at the given index.
pub fn field_at(&self, index: usize) -> Option<&UnnamedField> {
self.fields.get(index)
}
/// Iterate over the fields of this tuple.
pub fn iter(&self) -> Iter<'_, UnnamedField> {
self.fields.iter()
}
/// The total number of fields in this tuple.
pub fn field_len(&self) -> usize {
self.fields.len()
}
impl_type_methods!(ty);
/// The docstring of this tuple, if any.
#[cfg(feature = "documentation")]
pub fn docs(&self) -> Option<&'static str> {
self.docs
}
impl_generic_info_methods!(generics);
}
/// A tuple which allows fields to be added at runtime.
#[derive(Default, Debug)]
pub struct DynamicTuple {
represented_type: Option<&'static TypeInfo>,
fields: Vec<Box<dyn PartialReflect>>,
}
impl DynamicTuple {
/// Sets the [type] to be represented by this `DynamicTuple`.
///
/// # Panics
///
/// Panics if the given [type] is not a [`TypeInfo::Tuple`].
///
/// [type]: TypeInfo
pub fn set_represented_type(&mut self, represented_type: Option<&'static TypeInfo>) {
if let Some(represented_type) = represented_type {
assert!(
matches!(represented_type, TypeInfo::Tuple(_)),
"expected TypeInfo::Tuple but received: {:?}",
represented_type
);
}
self.represented_type = represented_type;
}
/// Appends an element with value `value` to the tuple.
pub fn insert_boxed(&mut self, value: Box<dyn PartialReflect>) {
self.represented_type = None;
self.fields.push(value);
}
/// Appends a typed element with value `value` to the tuple.
pub fn insert<T: PartialReflect>(&mut self, value: T) {
self.represented_type = None;
self.insert_boxed(Box::new(value));
}
}
impl Tuple for DynamicTuple {
#[inline]
fn field(&self, index: usize) -> Option<&dyn PartialReflect> {
self.fields.get(index).map(|field| &**field)
}
#[inline]
fn field_mut(&mut self, index: usize) -> Option<&mut dyn PartialReflect> {
self.fields.get_mut(index).map(|field| &mut **field)
}
#[inline]
fn field_len(&self) -> usize {
self.fields.len()
}
#[inline]
fn iter_fields(&self) -> TupleFieldIter {
TupleFieldIter {
tuple: self,
index: 0,
}
}
#[inline]
fn drain(self: Box<Self>) -> Vec<Box<dyn PartialReflect>> {
self.fields
}
#[inline]
fn clone_dynamic(&self) -> DynamicTuple {
DynamicTuple {
represented_type: self.represented_type,
fields: self
.fields
.iter()
.map(|value| value.clone_value())
.collect(),
}
}
}
impl PartialReflect for DynamicTuple {
#[inline]
fn get_represented_type_info(&self) -> Option<&'static TypeInfo> {
self.represented_type
}
#[inline]
fn into_partial_reflect(self: Box<Self>) -> Box<dyn PartialReflect> {
self
}
fn as_partial_reflect(&self) -> &dyn PartialReflect {
self
}
fn as_partial_reflect_mut(&mut self) -> &mut dyn PartialReflect {
self
}
fn try_into_reflect(self: Box<Self>) -> Result<Box<dyn Reflect>, Box<dyn PartialReflect>> {
Err(self)
}
fn try_as_reflect(&self) -> Option<&dyn Reflect> {
None
}
fn try_as_reflect_mut(&mut self) -> Option<&mut dyn Reflect> {
None
}
fn apply(&mut self, value: &dyn PartialReflect) {
tuple_apply(self, value);
}
#[inline]
fn reflect_kind(&self) -> ReflectKind {
ReflectKind::Tuple
}
#[inline]
fn reflect_ref(&self) -> ReflectRef {
ReflectRef::Tuple(self)
}
#[inline]
fn reflect_mut(&mut self) -> ReflectMut {
ReflectMut::Tuple(self)
}
#[inline]
fn reflect_owned(self: Box<Self>) -> ReflectOwned {
ReflectOwned::Tuple(self)
}
#[inline]
fn clone_value(&self) -> Box<dyn PartialReflect> {
Box::new(self.clone_dynamic())
}
fn try_apply(&mut self, value: &dyn PartialReflect) -> Result<(), ApplyError> {
tuple_try_apply(self, value)
}
fn reflect_partial_eq(&self, value: &dyn PartialReflect) -> Option<bool> {
tuple_partial_eq(self, value)
}
fn debug(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
write!(f, "DynamicTuple(")?;
tuple_debug(self, f)?;
write!(f, ")")
}
#[inline]
fn is_dynamic(&self) -> bool {
true
}
}
impl_type_path!((in bevy_reflect) DynamicTuple);
impl FromIterator<Box<dyn PartialReflect>> for DynamicTuple {
fn from_iter<I: IntoIterator<Item = Box<dyn PartialReflect>>>(fields: I) -> Self {
Self {
represented_type: None,
fields: fields.into_iter().collect(),
}
}
}
impl IntoIterator for DynamicTuple {
type Item = Box<dyn PartialReflect>;
type IntoIter = vec::IntoIter<Self::Item>;
fn into_iter(self) -> Self::IntoIter {
self.fields.into_iter()
}
}
impl<'a> IntoIterator for &'a DynamicTuple {
type Item = &'a dyn PartialReflect;
type IntoIter = TupleFieldIter<'a>;
fn into_iter(self) -> Self::IntoIter {
self.iter_fields()
}
}
/// Applies the elements of `b` to the corresponding elements of `a`.
///
/// # Panics
///
/// This function panics if `b` is not a tuple.
#[inline]
pub fn tuple_apply<T: Tuple>(a: &mut T, b: &dyn PartialReflect) {
if let Err(err) = tuple_try_apply(a, b) {
panic!("{err}");
}
}
/// Tries to apply the elements of `b` to the corresponding elements of `a` and
/// returns a Result.
///
/// # Errors
///
/// This function returns an [`ApplyError::MismatchedKinds`] if `b` is not a tuple or if
/// applying elements to each other fails.
#[inline]
pub fn tuple_try_apply<T: Tuple>(a: &mut T, b: &dyn PartialReflect) -> Result<(), ApplyError> {
let tuple = b.reflect_ref().as_tuple()?;
for (i, value) in tuple.iter_fields().enumerate() {
if let Some(v) = a.field_mut(i) {
v.try_apply(value)?;
}
}
Ok(())
}
/// Compares a [`Tuple`] with a [`PartialReflect`] value.
///
/// Returns true if and only if all of the following are true:
/// - `b` is a tuple;
/// - `b` has the same number of elements as `a`;
/// - [`PartialReflect::reflect_partial_eq`] returns `Some(true)` for pairwise elements of `a` and `b`.
///
/// Returns [`None`] if the comparison couldn't even be performed.
#[inline]
pub fn tuple_partial_eq<T: Tuple + ?Sized>(a: &T, b: &dyn PartialReflect) -> Option<bool> {
let ReflectRef::Tuple(b) = b.reflect_ref() else {
return Some(false);
};
if a.field_len() != b.field_len() {
return Some(false);
}
for (a_field, b_field) in a.iter_fields().zip(b.iter_fields()) {
let eq_result = a_field.reflect_partial_eq(b_field);
if let failed @ (Some(false) | None) = eq_result {
return failed;
}
}
Some(true)
}
/// The default debug formatter for [`Tuple`] types.
///
/// # Example
/// ```
/// use bevy_reflect::Reflect;
///
/// let my_tuple: &dyn Reflect = &(1, 2, 3);
/// println!("{:#?}", my_tuple);
///
/// // Output:
///
/// // (
/// // 1,
/// // 2,
/// // 3,
/// // )
/// ```
#[inline]
pub fn tuple_debug(dyn_tuple: &dyn Tuple, f: &mut Formatter<'_>) -> core::fmt::Result {
let mut debug = f.debug_tuple("");
for field in dyn_tuple.iter_fields() {
debug.field(&field as &dyn Debug);
}
debug.finish()
}
macro_rules! impl_reflect_tuple {
{$($index:tt : $name:tt),*} => {
impl<$($name: Reflect + MaybeTyped + TypePath + GetTypeRegistration),*> Tuple for ($($name,)*) {
#[inline]
fn field(&self, index: usize) -> Option<&dyn PartialReflect> {
match index {
$($index => Some(&self.$index as &dyn PartialReflect),)*
_ => None,
}
}
#[inline]
fn field_mut(&mut self, index: usize) -> Option<&mut dyn PartialReflect> {
match index {
$($index => Some(&mut self.$index as &mut dyn PartialReflect),)*
_ => None,
}
}
#[inline]
fn field_len(&self) -> usize {
let indices: &[usize] = &[$($index as usize),*];
indices.len()
}
#[inline]
fn iter_fields(&self) -> TupleFieldIter {
TupleFieldIter {
tuple: self,
index: 0,
}
}
#[inline]
fn drain(self: Box<Self>) -> Vec<Box<dyn PartialReflect>> {
vec![
$(Box::new(self.$index),)*
]
}
#[inline]
fn clone_dynamic(&self) -> DynamicTuple {
let info = self.get_represented_type_info();
DynamicTuple {
represented_type: info,
fields: self
.iter_fields()
.map(|value| value.clone_value())
.collect(),
}
}
}
impl<$($name: Reflect + MaybeTyped + TypePath + GetTypeRegistration),*> PartialReflect for ($($name,)*) {
fn get_represented_type_info(&self) -> Option<&'static TypeInfo> {
Some(<Self as Typed>::type_info())
}
#[inline]
fn into_partial_reflect(self: Box<Self>) -> Box<dyn PartialReflect> {
self
}
fn as_partial_reflect(&self) -> &dyn PartialReflect {
self
}
fn as_partial_reflect_mut(&mut self) -> &mut dyn PartialReflect {
self
}
fn try_into_reflect(self: Box<Self>) -> Result<Box<dyn Reflect>, Box<dyn PartialReflect>> {
Ok(self)
}
fn try_as_reflect(&self) -> Option<&dyn Reflect> {
Some(self)
}
fn try_as_reflect_mut(&mut self) -> Option<&mut dyn Reflect> {
Some(self)
}
fn reflect_kind(&self) -> ReflectKind {
ReflectKind::Tuple
}
fn reflect_ref(&self) -> ReflectRef {
ReflectRef::Tuple(self)
}
fn reflect_mut(&mut self) -> ReflectMut {
ReflectMut::Tuple(self)
}
fn reflect_owned(self: Box<Self>) -> ReflectOwned {
ReflectOwned::Tuple(self)
}
fn clone_value(&self) -> Box<dyn PartialReflect> {
Box::new(self.clone_dynamic())
}
fn reflect_partial_eq(&self, value: &dyn PartialReflect) -> Option<bool> {
crate::tuple_partial_eq(self, value)
}
fn apply(&mut self, value: &dyn PartialReflect) {
crate::tuple_apply(self, value);
}
fn try_apply(&mut self, value: &dyn PartialReflect) -> Result<(), ApplyError> {
crate::tuple_try_apply(self, value)
}
}
impl<$($name: Reflect + MaybeTyped + TypePath + GetTypeRegistration),*> Reflect for ($($name,)*) {
fn into_any(self: Box<Self>) -> Box<dyn Any> {
self
}
fn as_any(&self) -> &dyn Any {
self
}
fn as_any_mut(&mut self) -> &mut dyn Any {
self
}
fn into_reflect(self: Box<Self>) -> Box<dyn Reflect> {
self
}
fn as_reflect(&self) -> &dyn Reflect {
self
}
fn as_reflect_mut(&mut self) -> &mut dyn Reflect {
self
}
fn set(&mut self, value: Box<dyn Reflect>) -> Result<(), Box<dyn Reflect>> {
*self = value.take()?;
Ok(())
}
}
impl <$($name: Reflect + MaybeTyped + TypePath + GetTypeRegistration),*> Typed for ($($name,)*) {
fn type_info() -> &'static TypeInfo {
static CELL: $crate::utility::GenericTypeInfoCell = $crate::utility::GenericTypeInfoCell::new();
CELL.get_or_insert::<Self, _>(|| {
let fields = [
$(UnnamedField::new::<$name>($index),)*
];
let info = TupleInfo::new::<Self>(&fields);
TypeInfo::Tuple(info)
})
}
}
impl<$($name: Reflect + MaybeTyped + TypePath + GetTypeRegistration),*> GetTypeRegistration for ($($name,)*) {
fn get_type_registration() -> TypeRegistration {
TypeRegistration::of::<($($name,)*)>()
}
fn register_type_dependencies(_registry: &mut TypeRegistry) {
$(_registry.register::<$name>();)*
}
}
impl<$($name: FromReflect + MaybeTyped + TypePath + GetTypeRegistration),*> FromReflect for ($($name,)*)
{
fn from_reflect(reflect: &dyn PartialReflect) -> Option<Self> {
let _ref_tuple = reflect.reflect_ref().as_tuple().ok()?;
Some(
(
$(
<$name as FromReflect>::from_reflect(_ref_tuple.field($index)?)?,
)*
)
)
}
}
}
}
impl_reflect_tuple! {}
impl_reflect_tuple! {0: A}
impl_reflect_tuple! {0: A, 1: B}
impl_reflect_tuple! {0: A, 1: B, 2: C}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E, 5: F}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E, 5: F, 6: G}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E, 5: F, 6: G, 7: H}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E, 5: F, 6: G, 7: H, 8: I}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E, 5: F, 6: G, 7: H, 8: I, 9: J}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E, 5: F, 6: G, 7: H, 8: I, 9: J, 10: K}
impl_reflect_tuple! {0: A, 1: B, 2: C, 3: D, 4: E, 5: F, 6: G, 7: H, 8: I, 9: J, 10: K, 11: L}
macro_rules! impl_type_path_tuple {
($(#[$meta:meta])*) => {
$(#[$meta])*
impl TypePath for () {
fn type_path() -> &'static str {
"()"
}
fn short_type_path() -> &'static str {
"()"
}
}
};
($(#[$meta:meta])* $param:ident) => {
$(#[$meta])*
impl <$param: TypePath> TypePath for ($param,) {
fn type_path() -> &'static str {
use $crate::__macro_exports::alloc_utils::ToOwned;
static CELL: GenericTypePathCell = GenericTypePathCell::new();
CELL.get_or_insert::<Self, _>(|| {
"(".to_owned() + $param::type_path() + ",)"
})
}
fn short_type_path() -> &'static str {
use $crate::__macro_exports::alloc_utils::ToOwned;
static CELL: GenericTypePathCell = GenericTypePathCell::new();
CELL.get_or_insert::<Self, _>(|| {
"(".to_owned() + $param::short_type_path() + ",)"
})
}
}
};
($(#[$meta:meta])* $last:ident $(,$param:ident)*) => {
$(#[$meta])*
impl <$($param: TypePath,)* $last: TypePath> TypePath for ($($param,)* $last) {
fn type_path() -> &'static str {
use $crate::__macro_exports::alloc_utils::ToOwned;
static CELL: GenericTypePathCell = GenericTypePathCell::new();
CELL.get_or_insert::<Self, _>(|| {
"(".to_owned() $(+ $param::type_path() + ", ")* + $last::type_path() + ")"
})
}
fn short_type_path() -> &'static str {
use $crate::__macro_exports::alloc_utils::ToOwned;
static CELL: GenericTypePathCell = GenericTypePathCell::new();
CELL.get_or_insert::<Self, _>(|| {
"(".to_owned() $(+ $param::short_type_path() + ", ")* + $last::short_type_path() + ")"
})
}
}
};
}
all_tuples!(
#[doc(fake_variadic)]
impl_type_path_tuple,
0,
12,
P
);
#[cfg(feature = "functions")]
const _: () = {
macro_rules! impl_get_ownership_tuple {
($(#[$meta:meta])* $($name: ident),*) => {
$(#[$meta])*
$crate::func::args::impl_get_ownership!(($($name,)*); <$($name),*>);
};
}
all_tuples!(
#[doc(fake_variadic)]
impl_get_ownership_tuple,
0,
12,
P
);
macro_rules! impl_from_arg_tuple {
($(#[$meta:meta])* $($name: ident),*) => {
$(#[$meta])*
$crate::func::args::impl_from_arg!(($($name,)*); <$($name: FromReflect + MaybeTyped + TypePath + GetTypeRegistration),*>);
};
}
all_tuples!(
#[doc(fake_variadic)]
impl_from_arg_tuple,
0,
12,
P
);
macro_rules! impl_into_return_tuple {
($(#[$meta:meta])* $($name: ident),+) => {
$(#[$meta])*
$crate::func::impl_into_return!(($($name,)*); <$($name: FromReflect + MaybeTyped + TypePath + GetTypeRegistration),*>);
};
}
// The unit type (i.e. `()`) is special-cased, so we skip implementing it here.
all_tuples!(
#[doc(fake_variadic)]
impl_into_return_tuple,
1,
12,
P
);
};
#[cfg(test)]
mod tests {
use super::Tuple;
#[test]
fn next_index_increment() {
let mut iter = (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11).iter_fields();
let size = iter.len();
iter.index = size - 1;
let prev_index = iter.index;
assert!(iter.next().is_some());
assert_eq!(prev_index, iter.index - 1);
// When None we should no longer increase index
assert!(iter.next().is_none());
assert_eq!(size, iter.index);
assert!(iter.next().is_none());
assert_eq!(size, iter.index);
}
}