61 lines
1.7 KiB
Rust
61 lines
1.7 KiB
Rust
///! # Module support type-level programming
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///
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/// This module is more or less taken from the
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/// [ATSAMD HAL](https://docs.rs/atsamd-hal/0.13.0/atsamd_hal/typelevel/index.html).
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/// You can find a thorough explanation of the patterns used there.
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use crate::Sealed;
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/// Type-level version of the [None] variant
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#[derive(Default)]
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pub struct NoneT;
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impl Sealed for NoneT {}
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/// Marker trait for type identity
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///
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/// This trait is used as part of the [`AnyKind`](https://docs.rs/atsamd-hal/0.13.0/atsamd_hal/typelevel/index.html)
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/// trait pattern. It represents the concept of type identity, because all implementors have
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/// `<Self as Is>::Type == Self`. When used as a trait bound with a specific
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/// type, it guarantees that the corresponding type parameter is exactly the
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/// specific type. Stated differently, it guarantees that `T == Specific` in
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/// the following example.
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///
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/// ```
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/// where T: Is<Type = Specific>
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/// ```
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///
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/// Moreover, the super traits guarantee that any instance of or reference to a
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/// type `T` can be converted into the `Specific` type.
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///
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/// ```
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/// fn example<T>(mut any: T)
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/// where
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/// T: Is<Type = Specific>,
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/// {
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/// let specific_mut: &mut Specific = any.as_mut();
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/// let specific_ref: &Specific = any.as_ref();
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/// let specific: Specific = any.into();
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/// }
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/// ```
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///
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/// [`AnyKind`]: #anykind-trait-pattern
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pub trait Is
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where
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Self: Sealed,
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Self: From<IsType<Self>>,
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Self: Into<IsType<Self>>,
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Self: AsRef<IsType<Self>>,
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Self: AsMut<IsType<Self>>,
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{
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type Type;
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}
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/// Type alias for [`Is::Type`]
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pub type IsType<T> = <T as Is>::Type;
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impl<T> Is for T
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where
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T: Sealed + AsRef<T> + AsMut<T>,
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{
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type Type = T;
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}
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