Move fn read_adapter out of trait TryRngCore to rand (#1669)

Author: dhardy

CHANGELOG.md

@@ -14,6 +14,7 @@ You may also find the [Upgrade Guide](https://rust-random.github.io/book/update.
 - Rename fns `IndexedRandom::choose_multiple` -> `sample`, `choose_multiple_array` -> `sample_array`, `choose_multiple_weighted` -> `sample_weighted`, struct `SliceChooseIter` -> `IndexedSamples` and fns `IteratorRandom::choose_multiple` -> `sample`, `choose_multiple_fill` -> `sample_fill` (#1632)
 - Use Edition 2024 and MSRV 1.85 (#1653)
 - Let `Fill` be implemented for element types, not sliceable types (#1652)
+- Replace fn `TryRngCore::read_adapter(..) -> RngReadAdapter` with simpler struct `RngReader` (#1669)
 
 ### Additions
 - Add fns `IndexedRandom::choose_iter`, `choose_weighted_iter` (#1632)

rand_core/CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Relax `Sized` bound on impls of `SeedableRng` (#1641)
 - Move `rand_core::impls::*` to `rand_core::le` module (#1667)
 - Use Edition 2024 and MSRV 1.85 (#1668)
+- Remove fn `TryRngCore::read_adapter(..) -> RngReadAdapter` (replaced with `rand::RngReader`) (#1669)
 
 ## [0.9.3] — 2025-02-29
 ### Other

rand_core/src/lib.rs

@@ -207,15 +207,6 @@ pub trait TryRngCore {
     fn unwrap_mut(&mut self) -> UnwrapMut<'_, Self> {
         UnwrapMut(self)
     }
-
-    /// Convert an [`RngCore`] to a [`RngReadAdapter`].
-    #[cfg(feature = "std")]
-    fn read_adapter(&mut self) -> RngReadAdapter<'_, Self>
-    where
-        Self: Sized,
-    {
-        RngReadAdapter { inner: self }
-    }
 }
 
 // Note that, unfortunately, this blanket impl prevents us from implementing
@@ -543,40 +534,6 @@ pub trait SeedableRng: Sized {
     }
 }
 
-/// Adapter that enables reading through a [`io::Read`](std::io::Read) from a [`RngCore`].
-///
-/// # Examples
-///
-/// ```no_run
-/// # use std::{io, io::Read};
-/// # use std::fs::File;
-/// # use rand_core::{OsRng, TryRngCore};
-///
-/// io::copy(&mut OsRng.read_adapter().take(100), &mut File::create("/tmp/random.bytes").unwrap()).unwrap();
-/// ```
-#[cfg(feature = "std")]
-pub struct RngReadAdapter<'a, R: TryRngCore + ?Sized> {
-    inner: &'a mut R,
-}
-
-#[cfg(feature = "std")]
-impl<R: TryRngCore + ?Sized> std::io::Read for RngReadAdapter<'_, R> {
-    #[inline]
-    fn read(&mut self, buf: &mut [u8]) -> Result<usize, std::io::Error> {
-        self.inner
-            .try_fill_bytes(buf)
-            .map_err(|err| std::io::Error::other(std::format!("RNG error: {err}")))?;
-        Ok(buf.len())
-    }
-}
-
-#[cfg(feature = "std")]
-impl<R: TryRngCore + ?Sized> std::fmt::Debug for RngReadAdapter<'_, R> {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        f.debug_struct("ReadAdapter").finish()
-    }
-}
-
 #[cfg(test)]
 mod test {
     use super::*;

src/lib.rs

@@ -129,6 +129,41 @@ pub use rng::{Fill, Rng};
 #[cfg(feature = "thread_rng")]
 use crate::distr::{Distribution, StandardUniform};
 
+/// Adapter to support [`std::io::Read`] over a [`TryRngCore`]
+///
+/// # Examples
+///
+/// ```no_run
+/// use std::{io, io::Read};
+/// use std::fs::File;
+/// use rand::{rngs::OsRng, RngReader};
+///
+/// io::copy(
+///     &mut RngReader(OsRng).take(100),
+///     &mut File::create("/tmp/random.bytes").unwrap()
+/// ).unwrap();
+/// ```
+#[cfg(feature = "std")]
+pub struct RngReader<R: TryRngCore>(pub R);
+
+#[cfg(feature = "std")]
+impl<R: TryRngCore> std::io::Read for RngReader<R> {
+    #[inline]
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, std::io::Error> {
+        self.0
+            .try_fill_bytes(buf)
+            .map_err(|err| std::io::Error::other(std::format!("RNG error: {err}")))?;
+        Ok(buf.len())
+    }
+}
+
+#[cfg(feature = "std")]
+impl<R: TryRngCore> std::fmt::Debug for RngReader<R> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_tuple("RngReader").finish()
+    }
+}
+
 /// Generate a random value using the thread-local random number generator.
 ///
 /// This function is shorthand for <code>[rng()].[random()](Rng::random)</code>:
@@ -337,6 +372,24 @@ mod test {
         }
     }
 
+    #[cfg(feature = "std")]
+    #[test]
+    fn rng_reader() {
+        use std::io::Read;
+
+        let mut rng = StepRng(255, 1);
+        let mut buf = [0u8; 24];
+        let expected = [
+            255, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0,
+        ];
+
+        RngReader(&mut rng).read_exact(&mut buf).unwrap();
+        assert_eq!(&buf, &expected);
+
+        RngReader(StepRng(255, 1)).read_exact(&mut buf).unwrap();
+        assert_eq!(&buf, &expected);
+    }
+
     #[test]
     #[cfg(feature = "thread_rng")]
     fn test_random() {