Improve documentation

src/len_type.rs

@@ -48,7 +48,7 @@ pub trait LenType:
     const ZERO: Self;
     /// The one value of the integer type.
     const ONE: Self;
-    /// The maxiumum value of this type, as a usize.
+    /// The maximum value of this type, as a `usize`.
     const MAX: usize;
 
     /// An infallible conversion from `usize` to `LenT`.
@@ -72,28 +72,40 @@ impl_lentype!(
 
 macro_rules! impl_lentodefault {
     ($LenT:ty: $($len:literal),*) => {$(
-        impl LenToDefault for Const<$len> {
-            type Default = $LenT;
+        impl SmallestLenType for Const<$len> {
+            type Type = $LenT;
         }
     )*};
 }
 
+/// A struct to create individual types for mapping with [`SmallestLenType`].
+///
+/// See the documentation of [`DefaultLenType`] for a detailed explanation.
 pub struct Const<const N: usize>;
 
+/// A trait to map [`Const`] to it's respective [`LenType`].
+///
+/// See the documentation of [`DefaultLenType`] for a detailed explanation.
 #[diagnostic::on_unimplemented(
-    message = "Length `N` does not have a default LenType mapping",
+    message = "Length `N` does not have a default `LenType` mapping",
     note = "Provide the `LenType` explicitly, such as `usize`"
 )]
-pub trait LenToDefault {
-    type Default: LenType;
+pub trait SmallestLenType {
+    type Type: LenType;
 }
 
-pub type DefaultLenType<const N: usize> = <Const<N> as LenToDefault>::Default;
+/// A type alias to perform the `const N: usize` -> `LenType` mapping.
+///
+/// This is impossible to perform directly, but it is possible to write a `const N: usize` -> related `Type` mapping via a const generic argument,
+/// then map from that to an unrelated type via a trait with associated types.
+///
+/// [`Const`] is the "related type" in the above explaination, [`SmallestLenType`] is the mapping trait.
+pub type DefaultLenType<const N: usize> = <Const<N> as SmallestLenType>::Type;
 
 impl_lentodefault!(u8: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255);
 impl_lentodefault!(u16: 256, 300, 400, 500, 512, 600, 700, 800, 900, 1000, 1024, 2000, 2048, 4000, 4096, 8000, 8192, 16000, 16384, 32000, 32768, 65000, 65535);
 impl_lentodefault!(u32: 65536, 131072, 262144, 524288, 1048576, 2097152, 4194304, 8388608, 16777216, 33554432, 67108864, 134217728, 268435456, 536870912, 1073741824, 2147483648);
 
 pub const fn check_capacity_fits<LenT: LenType, const N: usize>() {
-    assert!(LenT::MAX >= N, "The capacity is larger than LenT can hold, increase the size of `LenT` or reduce the capacity")
+    assert!(LenT::MAX >= N, "The capacity is larger than `LenT` can hold, increase the size of `LenT` or reduce the capacity")
 }

src/string/mod.rs

@@ -213,6 +213,8 @@ impl<const N: usize> String<N> {
     #[inline]
     pub fn from_utf8<LenT: LenType>(vec: Vec<u8, N, LenT>) -> Result<Self, Utf8Error> {
         core::str::from_utf8(&vec)?;
+
+        // SAFETY: UTF-8 invariant has just been checked by `str::from_utf8`.
         Ok(unsafe { Self::from_utf8_unchecked(vec) })
     }
 

src/vec/mod.rs

@@ -190,6 +190,8 @@ impl<T, LenT: LenType, const N: usize> Vec<T, N, LenT> {
         const { check_capacity_fits::<NewLenT, N>() }
         let this = ManuallyDrop::new(self);
 
+        // SAFETY: Pointer argument is derived from a reference, meeting the safety documented invariants.
+        // This also prevents double drops by wrapping `self` in `ManuallyDrop`.
         Vec {
             len: NewLenT::from_usize(this.len()),
             buffer: unsafe { ptr::read(&this.buffer) },