From 89ec7ed9ee7d7c16cb947ce1f67282c14efa54e1 Mon Sep 17 00:00:00 2001
From: MM <mmayer@mayeranalytics.com>
Date: Wed, 13 Nov 2024 07:51:53 +0100
Subject: [PATCH] default impl in trait are not accessible?

---
 src/generic.rs | 164 ++++++++++++++++++++++++++++++++-----------------
 1 file changed, 107 insertions(+), 57 deletions(-)

diff --git a/src/generic.rs b/src/generic.rs
index 5c4e99d..ecaf32a 100644
--- a/src/generic.rs
+++ b/src/generic.rs
@@ -1,122 +1,172 @@
-/// Generic functions
+/// Generic functions `encode` and `decode` that taken an instance the `Encoding` trait.
+/// The encode and decode come also in the flavour Encoding::encode and Encoding::decode.
+/// 
+/// The point of the whole commotion is to have single generic encode<Encoding> and decode<Encoding>
+/// function that is better suited to generic programming than the wrappers codec::enc, dec, etc.
+///
+/// There are four such `Encoding` instances:
+/// - `StandardEncoding` for unsorted integer lists (using codec::dec and enc)
+/// - `IncreasingEncoding` for increasing integer lists (using codec::ddec and denc)
+/// - `StrictlyIncreasingEncoding` for strictly increasing integer lists (using codec::d1dec and d1enc)
+/// - `ZigZagEncoding` for unsorted integer lists (using codec::zdec and zenc)
+/// 
+/// Along with those two function we have `dec_buf_len` and `enc_buf_size` that are used to calculate
+/// the safe buffer sizes.
+/// 
+/// Each encoding gets an u8 identifier `ENC_TYPE` that can be used for lookup tables, etc.
+/// 
+/// The sample function is used to generate random data for testing the encodings.
 use crate::codec::*;
 use crate::sample::*;
 use std::marker::PhantomData;
-use rand::{
+use std::mem;
+use rand::{ // for testing
     prelude::Distribution, 
-    distributions::Standard
+    distributions::Standard,
 };
 
+pub trait EncodingBase {
+    type W: Width;
+}
+
+pub struct StandardEncodingBase<WT>           { _wt: PhantomData<WT> }
+pub struct IncreasingEncodingBase<WT>         { _wt: PhantomData<WT> }
+pub struct StrictlyIncreasingEncodingBase<WT> { _wt: PhantomData<WT> }
+pub struct ZigZagEncodingBase<WT>             { _wt: PhantomData<WT> }
+
+impl<WT:Width> EncodingBase for StandardEncodingBase<WT> { type W = WT; }
+impl<WT:Width> EncodingBase for IncreasingEncodingBase<WT> { type W = WT; }
+impl<WT:Width> EncodingBase for StrictlyIncreasingEncodingBase<WT> { type W = WT; }
+impl<WT:Width> EncodingBase for ZigZagEncodingBase<WT> { type W = WT; }
+
+/// Trait for encoding types with width.
 pub trait Encoding {
+    type W: Width;
     type T;
-    const ENC_TYPE: u8; // useful for identifying the encoding type in lookup tables, etc.
-    fn encode<EW: Width>(input: &[Self::T], output: &mut [u8]) -> usize;
-    fn decode<EW: Width>(input: &[u8], n: usize,  output: &mut [Self::T]) -> usize;
+    /// Numeric ID useful for identifying the encoding type in lookup tables, etc.
+    const ENC_TYPE: u8; 
+    /// Encode input data into output buffer
+    fn encode(input: &[Self::T], output: &mut [u8]) -> usize;
+    /// Decode input buffer into output data
+    fn decode(input: &[u8], n: usize,  output: &mut [Self::T]) -> usize;
+    /// Minimum safe [T] array length required for decoding n T's
+    fn dec_buf_len(n: usize) -> usize;
+    /// Minimum safe u8 size required for encoding n T's
+    fn enc_buf_size(n: usize) -> usize;
+    /// Sample random data for Self::T suitable for testing this encoding
     fn sample(len: usize) -> Vec<Self::T>;
 }
 
-pub struct StandardEncoding<W, T>           { _marker_w: PhantomData<W>, _marker_t: PhantomData<T> }
-pub struct IncreasingEncoding<W, T>         { _marker_w: PhantomData<W>, _marker_t: PhantomData<T> }
-pub struct StrictlyIncreasingEncoding<W, T> { _marker_w: PhantomData<W>, _marker_t: PhantomData<T> }
-pub struct ZigZagEncoding<W, T>             { _marker_w: PhantomData<W>, _marker_t: PhantomData<T> }
+pub struct StandardEncoding<WT, T>           { _marker_w: PhantomData<WT>, _marker_t: PhantomData<T> }
+pub struct IncreasingEncoding<WT, T>         { _marker_w: PhantomData<WT>, _marker_t: PhantomData<T> }
+pub struct StrictlyIncreasingEncoding<WT, T> { _marker_w: PhantomData<WT>, _marker_t: PhantomData<T> }
+pub struct ZigZagEncoding<WT, T>             { _marker_w: PhantomData<WT>, _marker_t: PhantomData<T> }
 
 // Implement the Encoding trait for each encoding type, linking to the right Codec methods
-impl<W: Width, T: Codec<W>> Encoding for StandardEncoding<W, T> 
+impl<WT: Width, T: Codec<WT>> Encoding for StandardEncoding<WT, T> 
     where Standard: Distribution<T>, T: Arithmetic
 {
+    type W = WT;
     type T = T;
     const ENC_TYPE: u8 = 0; // Example encoding type constant
-    fn encode<EW: Width>(input: &[Self::T], output: &mut [u8]) -> usize {
+    fn encode(input: &[Self::T], output: &mut [u8]) -> usize {
         T::enc(input, output)
     }
-    fn decode<EW: Width>(input: &[u8], n: usize, output: &mut [Self::T]) -> usize {
+    fn decode(input: &[u8], n: usize, output: &mut [Self::T]) -> usize {
         T::dec(input, n, output)
     }
+    fn dec_buf_len(n: usize) -> usize { Self::W::dec_buf_len::<Self::T>(n) }
+    fn enc_buf_size(n: usize) -> usize { Self::W::enc_buf_size::<Self::T>(n) }
     fn sample(len: usize) -> Vec<Self::T> { sample_standard(len) }
 } 
 
-impl<W: Width, T: Codec<W>> Encoding for IncreasingEncoding<W, T> 
+impl<WT: Width, T: Codec<WT>> Encoding for IncreasingEncoding<WT, T> 
 where Standard: Distribution<T>, T: Arithmetic
 {
+    type W = WT;
     type T = T;
     const ENC_TYPE: u8 = 1;
-    fn encode<EW: Width>(input: &[Self::T], output: &mut [u8]) -> usize {
+    fn encode(input: &[Self::T], output: &mut [u8]) -> usize {
         T::denc(input, output)
     }
-    fn decode<EW: Width>(input: &[u8], n: usize, output: &mut [Self::T]) -> usize {
+    fn decode(input: &[u8], n: usize, output: &mut [Self::T]) -> usize {
         T::ddec(input, n, output)
     }
+    fn dec_buf_len(n: usize) -> usize { Self::W::dec_buf_len::<Self::T>(n) }
+    fn enc_buf_size(n: usize) -> usize { Self::W::enc_buf_size::<Self::T>(n) }
     fn sample(len: usize) -> Vec<Self::T>
         where Standard: Distribution<T>, T: Arithmetic
     { sample_increasing(len, 0, 10) }
 }
 
-impl<W: Width, T: Codec<W>> Encoding for StrictlyIncreasingEncoding<W, T> 
+impl<WT: Width, T: Codec<WT>> Encoding for StrictlyIncreasingEncoding<WT, T> 
     where Standard: Distribution<T>, T: Arithmetic
 {
+    type W = WT;
     type T = T;
     const ENC_TYPE: u8 = 2;
-    fn encode<EW: Width>(input: &[Self::T], output: &mut [u8]) -> usize {
+    fn encode(input: &[Self::T], output: &mut [u8]) -> usize {
         T::d1enc(input, output)
     }
-    fn decode<EW: Width>(input: &[u8], n: usize, output: &mut [Self::T]) -> usize {
+    fn decode(input: &[u8], n: usize, output: &mut [Self::T]) -> usize {
         T::d1dec(input, n, output)
     }
+    fn dec_buf_len(n: usize) -> usize { Self::W::dec_buf_len::<Self::T>(n) }
+    fn enc_buf_size(n: usize) -> usize { Self::W::enc_buf_size::<Self::T>(n) }
     fn sample(len: usize) -> Vec<Self::T>
         where Standard: Distribution<T>, T: Arithmetic
     { sample_increasing(len, 1, 10) }
 }
 
-impl<W: Width, T: Codec<W>> Encoding for ZigZagEncoding<W, T> 
+impl<WT: Width, T: Codec<WT>> Encoding for ZigZagEncoding<WT, T> 
     where Standard: Distribution<T>, T: Arithmetic
 {
+    type W = WT;
     type T = T;
     const ENC_TYPE: u8 = 3;
-    fn encode<EW: Width>(input: &[Self::T], output: &mut [u8]) -> usize {
+    fn encode(input: &[Self::T], output: &mut [u8]) -> usize {
         T::zenc(input, output)
     }
-    fn decode<EW: Width>(input: &[u8], n: usize, output: &mut [Self::T]) -> usize {
+    fn decode(input: &[u8], n: usize, output: &mut [Self::T]) -> usize {
         T::zdec(input, n, output)
     }
+    fn dec_buf_len(n: usize) -> usize { Self::W::dec_buf_len::<Self::T>(n) }
+    fn enc_buf_size(n: usize) -> usize { Self::W::enc_buf_size::<Self::T>(n) }
     fn sample(len: usize) -> Vec<Self::T> { sample_standard(len) }
 }
 
 /// Generic encoding function
-pub fn encode<E: Encoding, W: Width>(input: &[E::T], output: &mut [u8]) -> usize {
-    E::encode::<W>(input, output)
+pub fn encode<E: Encoding>(input: &[E::T], output: &mut [u8]) -> usize {
+    E::encode(input, output)
 }
 
 /// Generic decoding function
-pub fn decode<E: Encoding, W: Width>(input: &[u8], n: usize, output: &mut [E::T]) -> usize {
-    E::decode::<W>(input, n, output)
+pub fn decode<E: Encoding>(input: &[u8], n: usize, output: &mut [E::T]) -> usize {
+    E::decode(input, n, output)
 }
 
 #[cfg(test)]
 use rand::Rng;
 
 #[cfg(test)]
-fn test_enc_dec_generic<T, E, WidthType>()
+fn test_enc_dec_generic<E>()
 where
-    WidthType: Width,
-    E: Encoding<T = T>,
-    T: Codec<WidthType>,
-    T: Eq + Clone + core::fmt::Debug + Default,
-    u8: Codec<WidthType>, u16: Codec<WidthType>, u32: Codec<WidthType>, u64: Codec<WidthType>,
-    Standard: Distribution<T>, T: Arithmetic
+    E: Encoding,
+    E::T : Default + std::fmt::Debug,
+    E::W : Width,
+    Standard: Distribution<E::T>, E::T: Arithmetic
 {
     let mut rng = rand::thread_rng();
     for _ in 0..256 {
         // Generate random input data
         let len = rng.gen_range(1..=16 * 1024);
-        let input: Vec<T> = E::sample(len);
-        println!("Input: {:?}", input);
+        let input: Vec<E::T> = E::sample(len);
         // Prepare input buffer and encode
-        let mut buf = vec![0u8; WidthType::enc_buf_size::<T>(input.len())];
-        let size_enc = encode::<E, WidthType>(&input, &mut buf);
+        let mut buf = vec![0u8; E::enc_buf_size(input.len())];
+        let size_enc = encode::<E>(&input, &mut buf);
         // Prepare output buffer and decode
-        let mut output: Vec<T> = vec![T::default(); WidthType::dec_buf_len::<T>(input.len())];
-        println!("Output: {:?}", output);
-        let size_dec = decode::<E, WidthType>(&buf[..size_enc], input.len(), &mut output);
+        let mut output: Vec<E::T> = vec![E::T::default(); E::dec_buf_len(input.len())];
+        let size_dec = decode::<E>(&buf[..size_enc], input.len(), &mut output);
         // Check results
         assert_eq!(size_enc, size_dec);
         assert_eq!(input, output[..input.len()]);
@@ -125,80 +175,80 @@ where
 
 #[test]
 fn test_enc_dec_u8_standard() {
-    test_enc_dec_generic::<u8, StandardEncoding<W, u8>, W>()
+    test_enc_dec_generic::<StandardEncoding<W, u8>>()
 }
 
 #[test]
 fn test_enc_dec_u16_standard() {
-    test_enc_dec_generic::<u16, StandardEncoding<W, u16>, W>()
+    test_enc_dec_generic::<StandardEncoding<W, u16>>()
 }
 
 #[test]
 fn test_enc_dec_u32_standard() {
-    test_enc_dec_generic::<u32, StandardEncoding<W, u32>, W>()
+    test_enc_dec_generic::<StandardEncoding<W, u32>>()
 }
 
 #[test]
 fn test_enc_dec_u64_standard() {
-    test_enc_dec_generic::<u64, StandardEncoding<W, u64>, W>()
+    test_enc_dec_generic::<StandardEncoding<W, u64>>()
 }
 
 #[test]
 fn test_enc_dec_u8_increasing() {
-    test_enc_dec_generic::<u8, IncreasingEncoding<W, u8>, W>()
+    test_enc_dec_generic::<IncreasingEncoding<W, u8>>()
 }
 
 #[test]
 fn test_enc_dec_u16_increasing() {
-    test_enc_dec_generic::<u16, IncreasingEncoding<W, u16>, W>()
+    test_enc_dec_generic::<IncreasingEncoding<W, u16>>()
 }
 
 #[test]
 fn test_enc_dec_u32_increasing() {
-    test_enc_dec_generic::<u32, IncreasingEncoding<W, u32>, W>()
+    test_enc_dec_generic::<IncreasingEncoding<W, u32>>()
 }
 
 #[test]
 fn test_enc_dec_u64_increasing() {
-    test_enc_dec_generic::<u64, IncreasingEncoding<W, u64>, W>()
+    test_enc_dec_generic::<IncreasingEncoding<W, u64>>()
 }
 
 #[test]
 fn test_enc_dec_u8_strictly_increasing() {
-    test_enc_dec_generic::<u8, StrictlyIncreasingEncoding<W, u8>, W>()
+    test_enc_dec_generic::<StrictlyIncreasingEncoding<W, u8>>()
 }
 
 #[test]
 fn test_enc_dec_u16_strictly_increasing() {
-    test_enc_dec_generic::<u16, StrictlyIncreasingEncoding<W, u16>, W>()
+    test_enc_dec_generic::<StrictlyIncreasingEncoding<W, u16>>()
 }
 
 #[test]
 fn test_enc_dec_u32_strictly_increasing() {
-    test_enc_dec_generic::<u32, StrictlyIncreasingEncoding<W, u32>, W>()
+    test_enc_dec_generic::<StrictlyIncreasingEncoding<W, u32>>()
 }
 
 #[test]
 fn test_enc_dec_u64_strictly_increasing() {
-    test_enc_dec_generic::<u64, StrictlyIncreasingEncoding<W, u64>, W>()
+    test_enc_dec_generic::<StrictlyIncreasingEncoding<W, u64>>()
 }
 
 #[test]
 fn test_enc_dec_u8_zigzag() {
-    test_enc_dec_generic::<u8, ZigZagEncoding<W, u8>, W>()
+    test_enc_dec_generic::<ZigZagEncoding<W, u8>>()
 }
 
 #[test]
 fn test_enc_dec_u16_zigzag() {
-    test_enc_dec_generic::<u16, ZigZagEncoding<W, u16>, W>()
+    test_enc_dec_generic::<ZigZagEncoding<W, u16>>()
 }
 
 #[test]
 fn test_enc_dec_u32_zigzag() {
-    test_enc_dec_generic::<u32, ZigZagEncoding<W, u32>, W>()
+    test_enc_dec_generic::<ZigZagEncoding<W, u32>>()
 }
 
 #[test]
 fn test_enc_dec_u64_zigzag() {
-    test_enc_dec_generic::<u64, ZigZagEncoding<W, u64>, W>()
-}
+    test_enc_dec_generic::<ZigZagEncoding<W, u64>>()
+}
\ No newline at end of file