Trait Enum 

pub trait Enum: PartialReflect {
    // Required methods
    fn field(&self, name: &str) -> Option<&(dyn PartialReflect + 'static)>;
    fn field_at(&self, index: usize) -> Option<&(dyn PartialReflect + 'static)>;
    fn field_mut(
        &mut self,
        name: &str,
    ) -> Option<&mut (dyn PartialReflect + 'static)>;
    fn field_at_mut(
        &mut self,
        index: usize,
    ) -> Option<&mut (dyn PartialReflect + 'static)>;
    fn index_of(&self, name: &str) -> Option<usize>;
    fn name_at(&self, index: usize) -> Option<&str>;
    fn iter_fields(&self) -> VariantFieldIter<'_> ;
    fn field_len(&self) -> usize;
    fn variant_name(&self) -> &str;
    fn variant_index(&self) -> usize;
    fn variant_type(&self) -> VariantType;

    // Provided methods
    fn to_dynamic_enum(&self) -> DynamicEnum { ... }
    fn is_variant(&self, variant_type: VariantType) -> bool { ... }
    fn variant_path(&self) -> String { ... }
    fn get_represented_enum_info(&self) -> Option<&'static EnumInfo> { ... }
}

A trait used to power enum-like operations via reflection.

This allows enums to be processed and modified dynamically at runtime without necessarily knowing the actual type. Enums are much more complex than their struct counterparts. As a result, users will need to be mindful of conventions, considerations, and complications when working with this trait.

Variants

An enum is a set of choices called variants. An instance of an enum can only exist as one of these choices at any given time. Consider Rust’s Option<T>. It’s an enum with two variants: None and Some. If you’re None, you can’t be Some and vice versa.

⚠️ This is very important: The Enum trait represents an enum as one of its variants. It does not represent the entire enum since that’s not true to how enums work.

Variants come in a few flavors:

Variant Type	Syntax
Unit	MyEnum::Foo
Tuple	MyEnum::Foo( i32, i32 )
Struct	MyEnum::Foo{ value: String }

As you can see, a unit variant contains no fields, while tuple and struct variants can contain one or more fields. The fields in a tuple variant is defined by their order within the variant. Index 0 represents the first field in the variant and so on. Fields in struct variants (excluding tuple structs), on the other hand, are represented by a name.

Implementation

💡 This trait can be automatically implemented using #[derive(Reflect)] on an enum definition.

Despite the fact that enums can represent multiple states, traits only exist in one state and must be applied to the entire enum rather than a particular variant. Because of this limitation, the Enum trait must not only represent any of the three variant types, but also define the methods for all three as well.

What does this mean? It means that even though a unit variant contains no fields, a representation of that variant using the Enum trait will still contain methods for accessing fields! Again, this is to account for all three variant types.

We recommend using the built-in #[derive(Reflect)] macro to automatically handle all the implementation details for you. However, if you must implement this trait manually, there are a few things to keep in mind…

Field Order

While tuple variants identify their fields by the order in which they are defined, struct variants identify fields by their name. However, both should allow access to fields by their defined order.

The reason all fields, regardless of variant type, need to be accessible by their order is due to field iteration. We need a way to iterate through each field in a variant, and the easiest way of achieving that is through the use of field order.

The derive macro adds proper struct variant handling for Enum::index_of, Enum::name_at and Enum::field_at[_mut] methods. The first two methods are required for all struct variant types. By convention, implementors should also handle the last method as well, but this is not a strict requirement.

Field Names

Implementors may choose to handle Enum::index_of, Enum::name_at, and Enum::field[_mut] for tuple variants by considering stringified usizes to be valid names (such as "3"). This isn’t wrong to do, but the convention set by the derive macro is that it isn’t supported. It’s preferred that these strings be converted to their proper usize representations and the Enum::field_at[_mut] methods be used instead.

Required Methods

fn field(&self, name: &str) -> Option<&(dyn PartialReflect + 'static)>

Returns a reference to the value of the field (in the current variant) with the given name.

For non-VariantType::Struct variants, this should return None.

fn field_at(&self, index: usize) -> Option<&(dyn PartialReflect + 'static)>

Returns a reference to the value of the field (in the current variant) at the given index.

fn field_mut( &mut self, name: &str, ) -> Option<&mut (dyn PartialReflect + 'static)>

Returns a mutable reference to the value of the field (in the current variant) with the given name.

For non-VariantType::Struct variants, this should return None.

fn field_at_mut( &mut self, index: usize, ) -> Option<&mut (dyn PartialReflect + 'static)>

Returns a mutable reference to the value of the field (in the current variant) at the given index.

fn index_of(&self, name: &str) -> Option<usize>

Returns the index of the field (in the current variant) with the given name.

For non-VariantType::Struct variants, this should return None.

fn name_at(&self, index: usize) -> Option<&str>

Returns the name of the field (in the current variant) with the given index.

For non-VariantType::Struct variants, this should return None.

fn iter_fields(&self) -> VariantFieldIter<'_>

Returns an iterator over the values of the current variant’s fields.

fn field_len(&self) -> usize

Returns the number of fields in the current variant.

fn variant_name(&self) -> &str

The name of the current variant.

fn variant_index(&self) -> usize

The index of the current variant.

fn variant_type(&self) -> VariantType

The type of the current variant.

Provided Methods

fn to_dynamic_enum(&self) -> DynamicEnum

Creates a new DynamicEnum from this enum.

fn is_variant(&self, variant_type: VariantType) -> bool

Returns true if the current variant’s type matches the given one.

fn variant_path(&self) -> String

Returns the full path to the current variant.

fn get_represented_enum_info(&self) -> Option<&'static EnumInfo>

Will return None if TypeInfo is not available.

Implementations on Foreign Types

impl<T> Enum for Option<T>

where Option<T>: Any + Send + Sync, T: TypePath + FromReflect + MaybeTyped + RegisterForReflection,

fn field(&self, __name_param: &str) -> Option<&(dyn PartialReflect + 'static)>

fn field_at( &self, __index_param: usize, ) -> Option<&(dyn PartialReflect + 'static)>

fn field_mut( &mut self, __name_param: &str, ) -> Option<&mut (dyn PartialReflect + 'static)>

fn field_at_mut( &mut self, __index_param: usize, ) -> Option<&mut (dyn PartialReflect + 'static)>

fn index_of(&self, __name_param: &str) -> Option<usize>

fn name_at(&self, __index_param: usize) -> Option<&str>

fn iter_fields(&self) -> VariantFieldIter<'_>

fn field_len(&self) -> usize

fn variant_name(&self) -> &str

fn variant_index(&self) -> usize

fn variant_type(&self) -> VariantType

fn to_dynamic_enum(&self) -> DynamicEnum

impl<T, E> Enum for Result<T, E>

where Result<T, E>: Any + Send + Sync, T: TypePath + FromReflect + MaybeTyped + RegisterForReflection, E: TypePath + FromReflect + MaybeTyped + RegisterForReflection,

fn field(&self, __name_param: &str) -> Option<&(dyn PartialReflect + 'static)>

fn field_at( &self, __index_param: usize, ) -> Option<&(dyn PartialReflect + 'static)>

fn field_mut( &mut self, __name_param: &str, ) -> Option<&mut (dyn PartialReflect + 'static)>

fn field_at_mut( &mut self, __index_param: usize, ) -> Option<&mut (dyn PartialReflect + 'static)>

fn index_of(&self, __name_param: &str) -> Option<usize>

fn name_at(&self, __index_param: usize) -> Option<&str>

fn iter_fields(&self) -> VariantFieldIter<'_>

fn field_len(&self) -> usize

fn variant_name(&self) -> &str

fn variant_index(&self) -> usize

fn variant_type(&self) -> VariantType

fn to_dynamic_enum(&self) -> DynamicEnum

Implementors

impl Enum for Tov

impl Enum for DynamicEnum