Struct Index 

pub struct Index<const I: usize>;

The Index type, a.k.a. δ, is used to represent a usize value at the type level.

Index is simply defined to be parameterized by a const-generic value of type usize. It is most often used to access generic fields by their index, instead of by their name.

Index is also shown as δ to improve the readability of compiler error messages.

Example

Given the following struct definition:

pub struct MyContext(pub u32);

The following HasField implementation would be generated, with use of Index<0> as the field tag:

impl HasField<Index<0>> for MyContext {
    type Value = u32;

    fn get_field(&self) -> &u32 {
        &self.0
    }
}

Trait Implementations

impl<const I: usize> Clone for δ<I>

fn clone(&self) -> δ<I>

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<const I: usize> Debug for δ<I>

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<const I: usize> Default for δ<I>

fn default() -> δ<I>

Returns the “default value” for a type.

impl<const I: usize> Display for δ<I>

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<const I: usize> PartialEq for δ<I>

fn eq(&self, other: &δ<I>) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<const I: usize> Copy for δ<I>

impl<const I: usize> Eq for δ<I>

impl<const I: usize> StructuralPartialEq for δ<I>