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38 lines
1.5 KiB
Rust
38 lines
1.5 KiB
Rust
//! Plain Old Data trait and blanket implementations.
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//!
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//! Types that implement [`Pod`] can be safely created by copying their raw byte
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//! representation. This is useful for reading on-disk structures from block
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//! devices.
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/// An unsafe trait indicating that a type is "Plain Old Data".
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///
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/// A type is `Pod` if it is a simple collection of bytes with no invalid bit
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/// patterns. This means it can be safely created by simply copying its byte
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/// representation from memory or a device.
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///
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/// # Safety
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///
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/// The implementor of this trait MUST guarantee that:
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/// 1. The type has a fixed, known layout. Using `#[repr(C)]` or
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/// `#[repr(transparent)]` is a must! The Rust ABI is unstable.
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/// 2. The type contains no padding bytes, or if it does, that reading those
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/// padding bytes as uninitialized memory is not undefined behavior.
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/// 3. All possible bit patterns for the type's size are valid instances of the type.
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/// For example, a `bool` is NOT `Pod` because its valid representations are only
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/// 0x00 and 0x01, not any other byte value. A `u32` is `Pod` because all
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/// 2^32 bit patterns are valid `u32` values.
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pub unsafe trait Pod: Sized {}
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// Blanket implementations for primitive types that are definitely Pod.
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unsafe impl Pod for u8 {}
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unsafe impl Pod for u16 {}
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unsafe impl Pod for u32 {}
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unsafe impl Pod for u64 {}
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unsafe impl Pod for u128 {}
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unsafe impl Pod for i8 {}
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unsafe impl Pod for i16 {}
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unsafe impl Pod for i32 {}
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unsafe impl Pod for i64 {}
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unsafe impl Pod for i128 {}
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unsafe impl<T: Pod, const N: usize> Pod for [T; N] {}
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