rename NoPadding to NoUninit and clarify docs (#95)

derive/src/lib.rs

@@ -9,7 +9,7 @@ use quote::{quote, quote_spanned};
 use syn::{parse_macro_input, DeriveInput, spanned::Spanned};
 
 use crate::traits::{
-  AnyBitPattern, Contiguous, Derivable, CheckedBitPattern, NoPadding, Pod, TransparentWrapper, Zeroable,
+  AnyBitPattern, Contiguous, Derivable, CheckedBitPattern, NoUninit, Pod, TransparentWrapper, Zeroable,
 };
 
 /// Derive the `Pod` trait for a struct
@@ -93,17 +93,17 @@ pub fn derive_zeroable(
   proc_macro::TokenStream::from(expanded)
 }
 
-/// Derive the `NoPadding` trait for a struct or enum
+/// Derive the `NoUninit` trait for a struct or enum
 ///
 /// The macro ensures that the type follows all the the safety requirements
-/// for the `NoPadding` trait.
+/// for the `NoUninit` trait.
 ///
 /// The following constraints need to be satisfied for the macro to succeed
-/// (the rest of the constraints are guaranteed by the `NoPadding` subtrait bounds,
+/// (the rest of the constraints are guaranteed by the `NoUninit` subtrait bounds,
 /// i.e. the type must be `Sized + Copy + 'static`):
 ///
 /// If applied to a struct:
-/// - All fields in the struct must implement `NoPadding`
+/// - All fields in the struct must implement `NoUninit`
 /// - The struct must be `#[repr(C)]` or `#[repr(transparent)]`
 /// - The struct must not contain any padding bytes
 /// - The struct must contain no generic parameters
@@ -112,12 +112,12 @@ pub fn derive_zeroable(
 /// - The enum must be explicit `#[repr(Int)]`
 /// - All variants must be fieldless
 /// - The enum must contain no generic parameters
-#[proc_macro_derive(NoPadding)]
+#[proc_macro_derive(NoUninit)]
-pub fn derive_no_padding(
+pub fn derive_no_uninit(
   input: proc_macro::TokenStream,
 ) -> proc_macro::TokenStream {
   let expanded =
-    derive_marker_trait::<NoPadding>(parse_macro_input!(input as DeriveInput));
+    derive_marker_trait::<NoUninit>(parse_macro_input!(input as DeriveInput));
 
   proc_macro::TokenStream::from(expanded)
 }
@@ -130,14 +130,14 @@ pub fn derive_no_padding(
 ///
 /// The following constraints need to be satisfied for the macro to succeed
 /// (the rest of the constraints are guaranteed by the `CheckedBitPattern` subtrait bounds,
-/// i.e. are guaranteed by the requirements of the `NoPadding` trait which `CheckedBitPattern`
+/// i.e. are guaranteed by the requirements of the `NoUninit` trait which `CheckedBitPattern`
 /// is a subtrait of):
 ///
 /// If applied to a struct:
 /// - All fields must implement `CheckedBitPattern`
 ///
 /// If applied to an enum:
-/// - All requirements already checked by `NoPadding`, just impls the trait
+/// - All requirements already checked by `NoUninit`, just impls the trait
 #[proc_macro_derive(CheckedBitPattern)]
 pub fn derive_maybe_pod(
   input: proc_macro::TokenStream,

derive/src/traits.rs

@@ -107,11 +107,11 @@ impl Derivable for Zeroable {
   }
 }
 
-pub struct NoPadding;
+pub struct NoUninit;
 
-impl Derivable for NoPadding {
+impl Derivable for NoUninit {
   fn ident() -> TokenStream {
-    quote!(::bytemuck::NoPadding)
+    quote!(::bytemuck::NoUninit)
   }
 
   fn check_attributes(
@@ -121,20 +121,20 @@ impl Derivable for NoPadding {
     match ty {
       Data::Struct(_) => match repr.as_deref() {
         Some("C" | "transparent") => Ok(()),
-        _ => Err("NoPadding derive requires the type to be #[repr(C)] or #[repr(transparent)]"),
+        _ => Err("NoUninit requires the struct to be #[repr(C)] or #[repr(transparent)]"),
       },
       Data::Enum(_) => if repr.map(|repr| repr.starts_with('u') || repr.starts_with('i')) == Some(true) {
         Ok(())
       } else {
-        Err("NoPadding requires the enum to be an explicit #[repr(Int)]")
+        Err("NoUninit requires the enum to be an explicit #[repr(Int)]")
       },
-      Data::Union(_) => Err("NoPadding cannot be derived for unions")
+      Data::Union(_) => Err("NoUninit can only be derived on enums and structs")
     }
   }
 
   fn asserts(input: &DeriveInput) -> Result<TokenStream, &'static str> {
     if !input.generics.params.is_empty() {
-      return Err("NoPadding cannot be derived for structs containing generic parameters because the padding requirements can't be verified for generic structs");
+      return Err("NoUninit cannot be derived for structs containing generic parameters because the padding requirements can't be verified for generic structs");
     }
 
     match &input.data {
@@ -150,12 +150,12 @@ impl Derivable for NoPadding {
       }
       Data::Enum(DataEnum { variants, .. }) => {
         if variants.iter().any(|variant| !variant.fields.is_empty()) {
-          Err("Only fieldless enums are supported for NoPadding")
+          Err("Only fieldless enums are supported for NoUninit")
         } else {
           Ok(quote!())
         }
       }
-      Data::Union(_) => Err("NoPadding cannot be derived for unions")
+      Data::Union(_) => Err("NoUninit cannot be derived for unions"), // shouldn't be possible since we already error in attribute check for this case
     }
   }
 
@@ -203,7 +203,7 @@ impl Derivable for CheckedBitPattern {
 
         Ok(assert_fields_are_maybe_pod)
       }
-      Data::Enum(_) => Ok(quote!()), // nothing needed, already guaranteed OK by NoPadding
+      Data::Enum(_) => Ok(quote!()), // nothing needed, already guaranteed OK by NoUninit
       Data::Union(_) => Err("Internal error in CheckedBitPattern derive"), // shouldn't be possible since we already error in attribute check for this case
     }
   }

derive/tests/basic.rs

@@ -1,7 +1,7 @@
 #![allow(dead_code)]
 
 use bytemuck::{
-  Contiguous, CheckedBitPattern, NoPadding, Pod, TransparentWrapper, Zeroable, AnyBitPattern,
+  AnyBitPattern, Contiguous, CheckedBitPattern, NoUninit, Pod, TransparentWrapper, Zeroable,
 };
 use std::marker::PhantomData;
 
@@ -51,9 +51,9 @@ enum ContiguousWithImplicitValues {
   E,
 }
 
-#[derive(Copy, Clone, NoPadding)]
+#[derive(Copy, Clone, NoUninit)]
 #[repr(C)]
-struct NoPaddingTest {
+struct NoUninitTest {
   a: u16,
   b: u16,
 }
@@ -66,7 +66,7 @@ union UnionTestAnyBitPattern {
 }
 
 #[repr(u8)]
-#[derive(Debug, Clone, Copy, NoPadding, CheckedBitPattern, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, NoUninit, CheckedBitPattern, PartialEq, Eq)]
 enum CheckedBitPatternEnumWithValues {
   A = 0,
   B = 1,
@@ -76,7 +76,7 @@ enum CheckedBitPatternEnumWithValues {
 }
 
 #[repr(i8)]
-#[derive(Clone, Copy, NoPadding, CheckedBitPattern)]
+#[derive(Clone, Copy, NoUninit, CheckedBitPattern)]
 enum CheckedBitPatternEnumWithImplicitValues {
   A = -10,
   B,
@@ -86,7 +86,7 @@ enum CheckedBitPatternEnumWithImplicitValues {
 }
 
 #[repr(u8)]
-#[derive(Debug, Clone, Copy, NoPadding, CheckedBitPattern, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, NoUninit, CheckedBitPattern, PartialEq, Eq)]
 enum CheckedBitPatternEnumNonContiguous {
   A = 1,
   B = 8,
@@ -95,7 +95,7 @@ enum CheckedBitPatternEnumNonContiguous {
   E = 56,
 }
 
-#[derive(Debug, Copy, Clone, NoPadding, CheckedBitPattern, PartialEq, Eq)]
+#[derive(Debug, Copy, Clone, NoUninit, CheckedBitPattern, PartialEq, Eq)]
 #[repr(C)]
 struct CheckedBitPatternStruct {
   a: u8,

src/allocation.rs

@@ -18,7 +18,7 @@ use core::convert::TryInto;
 
 /// As [`try_cast_box`](try_cast_box), but unwraps for you.
 #[inline]
-pub fn cast_box<A: NoPadding, B: AnyBitPattern>(input: Box<A>) -> Box<B> {
+pub fn cast_box<A: NoUninit, B: AnyBitPattern>(input: Box<A>) -> Box<B> {
   try_cast_box(input).map_err(|(e, _v)| e).unwrap()
 }
 
@@ -32,7 +32,7 @@ pub fn cast_box<A: NoPadding, B: AnyBitPattern>(input: Box<A>) -> Box<B> {
 ///   alignment.
 /// * The start and end size of the `Box` must have the exact same size.
 #[inline]
-pub fn try_cast_box<A: NoPadding, B: AnyBitPattern>(
+pub fn try_cast_box<A: NoUninit, B: AnyBitPattern>(
   input: Box<A>,
 ) -> Result<Box<B>, (PodCastError, Box<A>)> {
   if align_of::<A>() != align_of::<B>() {
@@ -139,7 +139,7 @@ pub fn zeroed_slice_box<T: Zeroable>(length: usize) -> Box<[T]> {
 
 /// As [`try_cast_vec`](try_cast_vec), but unwraps for you.
 #[inline]
-pub fn cast_vec<A: NoPadding, B: AnyBitPattern>(input: Vec<A>) -> Vec<B> {
+pub fn cast_vec<A: NoUninit, B: AnyBitPattern>(input: Vec<A>) -> Vec<B> {
   try_cast_vec(input).map_err(|(e, _v)| e).unwrap()
 }
 
@@ -156,7 +156,7 @@ pub fn cast_vec<A: NoPadding, B: AnyBitPattern>(input: Vec<A>) -> Vec<B> {
 ///   capacity and length get adjusted during transmutation, but for now it's
 ///   absolute.
 #[inline]
-pub fn try_cast_vec<A: NoPadding, B: AnyBitPattern>(
+pub fn try_cast_vec<A: NoUninit, B: AnyBitPattern>(
   input: Vec<A>,
 ) -> Result<Vec<B>, (PodCastError, Vec<A>)> {
   if align_of::<A>() != align_of::<B>() {
@@ -199,7 +199,7 @@ pub fn try_cast_vec<A: NoPadding, B: AnyBitPattern>(
 ///   assert_eq!(&vec_of_words[..], &[0x0005_0006, 0x0007_0008][..])
 /// }
 /// ```
-pub fn pod_collect_to_vec<A: NoPadding + AnyBitPattern, B: NoPadding + AnyBitPattern>(src: &[A]) -> Vec<B> {
+pub fn pod_collect_to_vec<A: NoUninit + AnyBitPattern, B: NoUninit + AnyBitPattern>(src: &[A]) -> Vec<B> {
   let src_size = size_of_val(src);
   // Note(Lokathor): dst_count is rounded up so that the dest will always be at
   // least as many bytes as the src.

src/anybitpattern.rs

@@ -3,9 +3,9 @@ use crate::{Pod, Zeroable};
 /// Marker trait for "plain old data" types that are valid for any bit pattern.
 ///
 /// The requirements for this is very similar to [`Pod`],
-/// except that it doesn't require that the type contains no padding bytes.
+/// except that it doesn't require that the type contains no uninit (or padding) bytes.
 /// This limits what you can do with a type of this kind, but also broadens the
-/// included types to `repr(C)` structs that contain padding. Notably, you can only cast
+/// included types to `repr(C)` `struct`s that contain padding as well as `union`s. Notably, you can only cast
 /// *immutable* references and *owned* values into [`AnyBitPattern`] types, not
 /// *mutable* references.
 ///
@@ -29,7 +29,7 @@ use crate::{Pod, Zeroable};
 /// 
 /// # Safety
 ///
-/// Similar to [`Pod`] except we disregard the rule about it must not contain padding.
+/// Similar to [`Pod`] except we disregard the rule about it must not contain uninit bytes.
 /// Still, this is a quite strong guarantee about a type, so *be careful* when
 /// implementing it manually.
 ///

src/checked.rs

@@ -1,7 +1,7 @@
 //! Checked versions of the casting functions exposed in crate root
 //! that support [`CheckedBitPattern`] types.
 
-use crate::{internal::{self, something_went_wrong}, NoPadding, AnyBitPattern};
+use crate::{internal::{self, something_went_wrong}, NoUninit, AnyBitPattern};
 
 /// A marker trait that allows types that have some invalid bit patterns to be used
 /// in places that otherwise require [`AnyBitPattern`] or [`Pod`] types by performing
@@ -33,7 +33,7 @@ use crate::{internal::{self, something_went_wrong}, NoPadding, AnyBitPattern};
 /// If manually implementing the trait, we can do something like so:
 ///
 /// ```rust
-/// use bytemuck::{CheckedBitPattern, NoPadding};
+/// use bytemuck::{CheckedBitPattern, NoUninit};
 ///
 /// #[repr(u32)]
 /// #[derive(Copy, Clone)]
@@ -54,16 +54,16 @@ use crate::{internal::{self, something_went_wrong}, NoPadding, AnyBitPattern};
 ///     }
 /// }
 /// 
-/// // It is often useful to also implement `NoPadding` on our `CheckedBitPattern` types.
+/// // It is often useful to also implement `NoUninit` on our `CheckedBitPattern` types.
 /// // This will allow us to do casting of mutable references (and mutable slices).
 /// // It is not always possible to do so, but in this case we have no padding so it is.
-/// unsafe impl NoPadding for MyEnum {}
+/// unsafe impl NoUninit for MyEnum {}
 /// ```
 ///
 /// We can now use relevant casting functions. For example,
 ///
 /// ```rust
-/// # use bytemuck::{CheckedBitPattern, NoPadding};
+/// # use bytemuck::{CheckedBitPattern, NoUninit};
 /// # #[repr(u32)]
 /// # #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 /// # enum MyEnum {
@@ -71,7 +71,7 @@ use crate::{internal::{self, something_went_wrong}, NoPadding, AnyBitPattern};
 /// #     Variant1 = 1,
 /// #     Variant2 = 2,
 /// # }
-/// # unsafe impl NoPadding for MyEnum {}
+/// # unsafe impl NoUninit for MyEnum {}
 /// # unsafe impl CheckedBitPattern for MyEnum {
 /// #     type Bits = u32;
 /// #     fn is_valid_bit_pattern(bits: &u32) -> bool {
@@ -93,8 +93,8 @@ use crate::{internal::{self, something_went_wrong}, NoPadding, AnyBitPattern};
 /// let result = checked::try_from_bytes::<MyEnum>(bytes);
 /// assert!(result.is_err());
 /// 
-/// // Since we implemented NoPadding, we can also cast mutably from an original type
+/// // Since we implemented NoUninit, we can also cast mutably from an original type
-/// // that is `NoPadding + AnyBitPattern`:
+/// // that is `NoUninit + AnyBitPattern`:
 /// let mut my_u32 = 2u32;
 /// {
 ///   let as_enum_mut = checked::cast_mut::<_, MyEnum>(&mut my_u32);
@@ -214,7 +214,7 @@ pub fn try_from_bytes<T: CheckedBitPattern>(
 /// * If the slice's length isn’t exactly the size of the new type
 /// * If the slice contains an invalid bit pattern for `T`
 #[inline]
-pub fn try_from_bytes_mut<T: CheckedBitPattern + NoPadding>(
+pub fn try_from_bytes_mut<T: CheckedBitPattern + NoUninit>(
   s: &mut [u8],
 ) -> Result<&mut T, CheckedCastError> {
   let pod = unsafe { internal::try_from_bytes_mut(s) }?;
@@ -254,7 +254,7 @@ pub fn try_pod_read_unaligned<T: CheckedBitPattern>(bytes: &[u8]) -> Result<T, C
 /// * If the types don't have the same size this fails.
 /// * If `a` contains an invalid bit pattern for `B` this fails.
 #[inline]
-pub fn try_cast<A: NoPadding, B: CheckedBitPattern>(
+pub fn try_cast<A: NoUninit, B: CheckedBitPattern>(
   a: A,
 ) -> Result<B, CheckedCastError> {
   let pod = unsafe { internal::try_cast(a) }?;
@@ -274,7 +274,7 @@ pub fn try_cast<A: NoPadding, B: CheckedBitPattern>(
 /// * If the source type and target type aren't the same size.
 /// * If `a` contains an invalid bit pattern for `B` this fails.
 #[inline]
-pub fn try_cast_ref<A: NoPadding, B: CheckedBitPattern>(
+pub fn try_cast_ref<A: NoUninit, B: CheckedBitPattern>(
   a: &A,
 ) -> Result<&B, CheckedCastError> {
   let pod = unsafe { internal::try_cast_ref(a) }?;
@@ -290,7 +290,7 @@ pub fn try_cast_ref<A: NoPadding, B: CheckedBitPattern>(
 ///
 /// As [`checked_cast_ref`], but `mut`.
 #[inline]
-pub fn try_cast_mut<A: NoPadding + AnyBitPattern, B: CheckedBitPattern + NoPadding>(
+pub fn try_cast_mut<A: NoUninit + AnyBitPattern, B: CheckedBitPattern + NoUninit>(
   a: &mut A,
 ) -> Result<&mut B, CheckedCastError> {
   let pod = unsafe { internal::try_cast_mut(a) }?;
@@ -319,7 +319,7 @@ pub fn try_cast_mut<A: NoPadding + AnyBitPattern, B: CheckedBitPattern + NoPaddi
 ///   and a non-ZST.
 /// * If any element of the converted slice would contain an invalid bit pattern for `B` this fails.
 #[inline]
-pub fn try_cast_slice<A: NoPadding, B: CheckedBitPattern>(
+pub fn try_cast_slice<A: NoUninit, B: CheckedBitPattern>(
   a: &[A],
 ) -> Result<&[B], CheckedCastError> {
   let pod = unsafe { internal::try_cast_slice(a) }?;
@@ -338,7 +338,7 @@ pub fn try_cast_slice<A: NoPadding, B: CheckedBitPattern>(
 ///
 /// As [`checked_cast_slice`], but `&mut`.
 #[inline]
-pub fn try_cast_slice_mut<A: NoPadding + AnyBitPattern, B: CheckedBitPattern + NoPadding>(
+pub fn try_cast_slice_mut<A: NoUninit + AnyBitPattern, B: CheckedBitPattern + NoUninit>(
   a: &mut [A],
 ) -> Result<&mut [B], CheckedCastError> {
   let pod = unsafe { internal::try_cast_slice_mut(a) }?;
@@ -371,7 +371,7 @@ pub fn from_bytes<T: CheckedBitPattern>(s: &[u8]) -> &T {
 ///
 /// This is [`try_from_bytes_mut`] but will panic on error.
 #[inline]
-pub fn from_bytes_mut<T: NoPadding + CheckedBitPattern>(s: &mut [u8]) -> &mut T {
+pub fn from_bytes_mut<T: NoUninit + CheckedBitPattern>(s: &mut [u8]) -> &mut T {
   match try_from_bytes_mut(s) {
     Ok(t) => t,
     Err(e) => something_went_wrong("from_bytes_mut", e),
@@ -396,7 +396,7 @@ pub fn pod_read_unaligned<T: AnyBitPattern>(bytes: &[u8]) -> T {
 ///
 /// * This is like [`try_cast`](try_cast), but will panic on a size mismatch.
 #[inline]
-pub fn cast<A: NoPadding, B: CheckedBitPattern>(a: A) -> B {
+pub fn cast<A: NoUninit, B: CheckedBitPattern>(a: A) -> B {
   match try_cast(a) {
     Ok(t) => t,
     Err(e) => something_went_wrong("cast", e),
@@ -409,7 +409,7 @@ pub fn cast<A: NoPadding, B: CheckedBitPattern>(a: A) -> B {
 ///
 /// This is [`try_cast_mut`] but will panic on error.
 #[inline]
-pub fn cast_mut<A: NoPadding + AnyBitPattern, B: NoPadding + CheckedBitPattern>(a: &mut A) -> &mut B {
+pub fn cast_mut<A: NoUninit + AnyBitPattern, B: NoUninit + CheckedBitPattern>(a: &mut A) -> &mut B {
   match try_cast_mut(a) {
     Ok(t) => t,
     Err(e) => something_went_wrong("cast_mut", e),
@@ -422,7 +422,7 @@ pub fn cast_mut<A: NoPadding + AnyBitPattern, B: NoPadding + CheckedBitPattern>(
 ///
 /// This is [`try_cast_ref`] but will panic on error.
 #[inline]
-pub fn cast_ref<A: NoPadding, B: CheckedBitPattern>(a: &A) -> &B {
+pub fn cast_ref<A: NoUninit, B: CheckedBitPattern>(a: &A) -> &B {
   match try_cast_ref(a) {
     Ok(t) => t,
     Err(e) => something_went_wrong("cast_ref", e),
@@ -435,7 +435,7 @@ pub fn cast_ref<A: NoPadding, B: CheckedBitPattern>(a: &A) -> &B {
 ///
 /// This is [`try_cast_slice`] but will panic on error.
 #[inline]
-pub fn cast_slice<A: NoPadding, B: CheckedBitPattern>(a: &[A]) -> &[B] {
+pub fn cast_slice<A: NoUninit, B: CheckedBitPattern>(a: &[A]) -> &[B] {
   match try_cast_slice(a) {
     Ok(t) => t,
     Err(e) => something_went_wrong("cast_slice", e),
@@ -448,7 +448,7 @@ pub fn cast_slice<A: NoPadding, B: CheckedBitPattern>(a: &[A]) -> &[B] {
 ///
 /// This is [`try_cast_slice_mut`] but will panic on error.
 #[inline]
-pub fn cast_slice_mut<A: NoPadding + AnyBitPattern, B: NoPadding + CheckedBitPattern>(a: &mut [A]) -> &mut [B] {
+pub fn cast_slice_mut<A: NoUninit + AnyBitPattern, B: NoUninit + CheckedBitPattern>(a: &mut [A]) -> &mut [B] {
   match try_cast_slice_mut(a) {
     Ok(t) => t,
     Err(e) => something_went_wrong("cast_slice_mut", e),

src/lib.rs

@@ -94,8 +94,8 @@ pub use zeroable::*;
 mod pod;
 pub use pod::*;
 
-mod nopadding;
+mod no_uninit;
-pub use nopadding::*;
+pub use no_uninit::*;
 
 mod contiguous;
 pub use contiguous::*;
@@ -108,7 +108,7 @@ pub use transparent::*;
 
 #[cfg(feature = "derive")]
 pub use bytemuck_derive::{
-  AnyBitPattern, Contiguous, CheckedBitPattern, NoPadding, Pod, TransparentWrapper, Zeroable,
+  AnyBitPattern, Contiguous, CheckedBitPattern, NoUninit, Pod, TransparentWrapper, Zeroable,
 };
 
 /// The things that can go wrong when casting between [`Pod`] data forms.
@@ -147,7 +147,7 @@ impl std::error::Error for PodCastError {}
 /// Any ZST becomes an empty slice, and in that case the pointer value of that
 /// empty slice might not match the pointer value of the input reference.
 #[inline]
-pub fn bytes_of<T: NoPadding>(t: &T) -> &[u8] {
+pub fn bytes_of<T: NoUninit>(t: &T) -> &[u8] {
   unsafe { internal::bytes_of(t) }
 }
 
@@ -156,7 +156,7 @@ pub fn bytes_of<T: NoPadding>(t: &T) -> &[u8] {
 /// Any ZST becomes an empty slice, and in that case the pointer value of that
 /// empty slice might not match the pointer value of the input reference.
 #[inline]
-pub fn bytes_of_mut<T: NoPadding + AnyBitPattern>(t: &mut T) -> &mut [u8] {
+pub fn bytes_of_mut<T: NoUninit + AnyBitPattern>(t: &mut T) -> &mut [u8] {
   unsafe { internal::bytes_of_mut(t) }
 }
 
@@ -176,7 +176,7 @@ pub fn from_bytes<T: AnyBitPattern>(s: &[u8]) -> &T {
 ///
 /// This is [`try_from_bytes_mut`] but will panic on error.
 #[inline]
-pub fn from_bytes_mut<T: NoPadding + AnyBitPattern>(s: &mut [u8]) -> &mut T {
+pub fn from_bytes_mut<T: NoUninit + AnyBitPattern>(s: &mut [u8]) -> &mut T {
   unsafe { internal::from_bytes_mut(s) }
 }
 
@@ -216,7 +216,7 @@ pub fn try_from_bytes<T: AnyBitPattern>(s: &[u8]) -> Result<&T, PodCastError> {
 /// * If the slice isn't aligned for the new type
 /// * If the slice's length isn’t exactly the size of the new type
 #[inline]
-pub fn try_from_bytes_mut<T: NoPadding + AnyBitPattern>(
+pub fn try_from_bytes_mut<T: NoUninit + AnyBitPattern>(
   s: &mut [u8],
 ) -> Result<&mut T, PodCastError> {
   unsafe { internal::try_from_bytes_mut(s) }
@@ -228,7 +228,7 @@ pub fn try_from_bytes_mut<T: NoPadding + AnyBitPattern>(
 ///
 /// * This is like [`try_cast`](try_cast), but will panic on a size mismatch.
 #[inline]
-pub fn cast<A: NoPadding, B: AnyBitPattern>(a: A) -> B {
+pub fn cast<A: NoUninit, B: AnyBitPattern>(a: A) -> B {
   unsafe { internal::cast(a) }
 }
 
@@ -238,7 +238,7 @@ pub fn cast<A: NoPadding, B: AnyBitPattern>(a: A) -> B {
 ///
 /// This is [`try_cast_mut`] but will panic on error.
 #[inline]
-pub fn cast_mut<A: NoPadding + AnyBitPattern, B: NoPadding + AnyBitPattern>(a: &mut A) -> &mut B {
+pub fn cast_mut<A: NoUninit + AnyBitPattern, B: NoUninit + AnyBitPattern>(a: &mut A) -> &mut B {
   unsafe { internal::cast_mut(a) }
 }
 
@@ -248,7 +248,7 @@ pub fn cast_mut<A: NoPadding + AnyBitPattern, B: NoPadding + AnyBitPattern>(a: &
 ///
 /// This is [`try_cast_ref`] but will panic on error.
 #[inline]
-pub fn cast_ref<A: NoPadding, B: AnyBitPattern>(a: &A) -> &B {
+pub fn cast_ref<A: NoUninit, B: AnyBitPattern>(a: &A) -> &B {
   unsafe { internal::cast_ref(a) }
 }
 
@@ -258,7 +258,7 @@ pub fn cast_ref<A: NoPadding, B: AnyBitPattern>(a: &A) -> &B {
 ///
 /// This is [`try_cast_slice`] but will panic on error.
 #[inline]
-pub fn cast_slice<A: NoPadding, B: AnyBitPattern>(a: &[A]) -> &[B] {
+pub fn cast_slice<A: NoUninit, B: AnyBitPattern>(a: &[A]) -> &[B] {
   unsafe { internal::cast_slice(a) }
 }
 
@@ -268,19 +268,19 @@ pub fn cast_slice<A: NoPadding, B: AnyBitPattern>(a: &[A]) -> &[B] {
 ///
 /// This is [`try_cast_slice_mut`] but will panic on error.
 #[inline]
-pub fn cast_slice_mut<A: NoPadding + AnyBitPattern, B: NoPadding + AnyBitPattern>(a: &mut [A]) -> &mut [B] {
+pub fn cast_slice_mut<A: NoUninit + AnyBitPattern, B: NoUninit + AnyBitPattern>(a: &mut [A]) -> &mut [B] {
   unsafe { internal::cast_slice_mut(a) }
 }
 
 /// As `align_to`, but safe because of the [`Pod`] bound.
 #[inline]
-pub fn pod_align_to<T: NoPadding, U: AnyBitPattern>(vals: &[T]) -> (&[T], &[U], &[T]) {
+pub fn pod_align_to<T: NoUninit, U: AnyBitPattern>(vals: &[T]) -> (&[T], &[U], &[T]) {
   unsafe { vals.align_to::<U>() }
 }
 
 /// As `align_to_mut`, but safe because of the [`Pod`] bound.
 #[inline]
-pub fn pod_align_to_mut<T: NoPadding + AnyBitPattern, U: NoPadding + AnyBitPattern>(
+pub fn pod_align_to_mut<T: NoUninit + AnyBitPattern, U: NoUninit + AnyBitPattern>(
   vals: &mut [T],
 ) -> (&mut [T], &mut [U], &mut [T]) {
   unsafe { vals.align_to_mut::<U>() }
@@ -297,7 +297,7 @@ pub fn pod_align_to_mut<T: NoPadding + AnyBitPattern, U: NoPadding + AnyBitPatte
 ///
 /// * If the types don't have the same size this fails.
 #[inline]
-pub fn try_cast<A: NoPadding, B: AnyBitPattern>(a: A) -> Result<B, PodCastError> {
+pub fn try_cast<A: NoUninit, B: AnyBitPattern>(a: A) -> Result<B, PodCastError> {
   unsafe { internal::try_cast(a) }
 }
 
@@ -308,7 +308,7 @@ pub fn try_cast<A: NoPadding, B: AnyBitPattern>(a: A) -> Result<B, PodCastError>
 /// * If the reference isn't aligned in the new type
 /// * If the source type and target type aren't the same size.
 #[inline]
-pub fn try_cast_ref<A: NoPadding, B: AnyBitPattern>(a: &A) -> Result<&B, PodCastError> {
+pub fn try_cast_ref<A: NoUninit, B: AnyBitPattern>(a: &A) -> Result<&B, PodCastError> {
   unsafe { internal::try_cast_ref(a) }
 }
 
@@ -316,7 +316,7 @@ pub fn try_cast_ref<A: NoPadding, B: AnyBitPattern>(a: &A) -> Result<&B, PodCast
 ///
 /// As [`try_cast_ref`], but `mut`.
 #[inline]
-pub fn try_cast_mut<A: NoPadding + AnyBitPattern, B: NoPadding + AnyBitPattern>(a: &mut A) -> Result<&mut B, PodCastError> {
+pub fn try_cast_mut<A: NoUninit + AnyBitPattern, B: NoUninit + AnyBitPattern>(a: &mut A) -> Result<&mut B, PodCastError> {
   unsafe { internal::try_cast_mut(a) }
 }
 
@@ -336,7 +336,7 @@ pub fn try_cast_mut<A: NoPadding + AnyBitPattern, B: NoPadding + AnyBitPattern>(
 /// * Similarly, you can't convert between a [ZST](https://doc.rust-lang.org/nomicon/exotic-sizes.html#zero-sized-types-zsts)
 ///   and a non-ZST.
 #[inline]
-pub fn try_cast_slice<A: NoPadding, B: AnyBitPattern>(a: &[A]) -> Result<&[B], PodCastError> {
+pub fn try_cast_slice<A: NoUninit, B: AnyBitPattern>(a: &[A]) -> Result<&[B], PodCastError> {
   unsafe { internal::try_cast_slice(a) }
 }
 
@@ -345,7 +345,7 @@ pub fn try_cast_slice<A: NoPadding, B: AnyBitPattern>(a: &[A]) -> Result<&[B], P
 ///
 /// As [`try_cast_slice`], but `&mut`.
 #[inline]
-pub fn try_cast_slice_mut<A: NoPadding + AnyBitPattern, B: NoPadding + AnyBitPattern>(
+pub fn try_cast_slice_mut<A: NoUninit + AnyBitPattern, B: NoUninit + AnyBitPattern>(
   a: &mut [A],
 ) -> Result<&mut [B], PodCastError> {
   unsafe { internal::try_cast_slice_mut(a) }

src/no_uninit.rs

@@ -1,23 +1,23 @@
 use crate::Pod;
 
-/// Marker trait for "plain old data" types with no padding.
+/// Marker trait for "plain old data" types with no uninit (or padding) bytes.
 ///
 /// The requirements for this is very similar to [`Pod`],
 /// except that it doesn't require that all bit patterns of the type are valid, i.e.
 /// it does not require the type to be [`Zeroable`][crate::Zeroable].
 /// This limits what you can do with a type of this kind, but also broadens the
 /// included types to things like C-style enums. Notably, you can only cast from
-/// *immutable* references to a [`NoPadding`] type into *immutable* references of any other
+/// *immutable* references to a [`NoUninit`] type into *immutable* references of any other
 /// type, no casting of mutable references or mutable references to slices etc.
 ///
-/// [`Pod`] is a subset of [`NoPadding`], meaning that any `T: Pod` is also
+/// [`Pod`] is a subset of [`NoUninit`], meaning that any `T: Pod` is also
-/// [`NoPadding`] but any `T: NoPadding` is not necessarily [`Pod`]. If possible,
+/// [`NoUninit`] but any `T: NoUninit` is not necessarily [`Pod`]. If possible,
 /// prefer implementing [`Pod`] directly. To get more [`Pod`]-like functionality for
-/// a type that is only [`NoPadding`], consider also implementing [`CheckedBitPattern`][crate::CheckedBitPattern].
+/// a type that is only [`NoUninit`], consider also implementing [`CheckedBitPattern`][crate::CheckedBitPattern].
 ///
 /// # Derive
 ///
-/// A `#[derive(NoPadding)]` macro is provided under the `derive` feature flag which will
+/// A `#[derive(NoUninit)]` macro is provided under the `derive` feature flag which will
 /// automatically validate the requirements of this trait and implement the
 /// trait for you for both enums and structs. This is the recommended method for
 /// implementing the trait, however it's also possible to do manually. If you
@@ -32,21 +32,21 @@ use crate::Pod;
 ///
 /// * The type must be inhabited (eg: no
 ///   [Infallible](core::convert::Infallible)).
-/// * The type must not contain any padding bytes, either in the middle or on
+/// * The type must not contain any uninit (or padding) bytes, either in the middle or on
 ///   the end (eg: no `#[repr(C)] struct Foo(u8, u16)`, which has padding in the
 ///   middle, and also no `#[repr(C)] struct Foo(u16, u8)`, which has padding on
 ///   the end).
-/// * Structs need to have all fields also be `NoPadding`.
+/// * Structs need to have all fields also be `NoUninit`.
 /// * Structs need to be `repr(C)` or `repr(transparent)`. In the case of
 ///   `repr(C)`, the `packed` and `align` repr modifiers can be used as long as
 ///   all other rules end up being followed.
 /// * Enums need to have an explicit `#[repr(Int)]`
 /// * Enums must have only fieldless variants
 /// * There's probably more, don't mess it up (I mean it).
-pub unsafe trait NoPadding: Sized + Copy + 'static {}
+pub unsafe trait NoUninit: Sized + Copy + 'static {}
 
-unsafe impl<T: Pod> NoPadding for T {}
+unsafe impl<T: Pod> NoUninit for T {}
 
-unsafe impl NoPadding for char {}
+unsafe impl NoUninit for char {}
 
-unsafe impl NoPadding for bool {}
+unsafe impl NoUninit for bool {}

src/pod.rs

@@ -18,7 +18,7 @@ use super::*;
 ///   [Infallible](core::convert::Infallible)).
 /// * The type must allow any bit pattern (eg: no `bool` or `char`, which have
 ///   illegal bit patterns).
-/// * The type must not contain any padding bytes, either in the middle or on
+/// * The type must not contain any uninit (or padding) bytes, either in the middle or on
 ///   the end (eg: no `#[repr(C)] struct Foo(u8, u16)`, which has padding in the
 ///   middle, and also no `#[repr(C)] struct Foo(u16, u8)`, which has padding on
 ///   the end).