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Support ?Sized types in Rng*: TryRng* blanket impls #51

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Merged
dhardy merged 2 commits into from
Jan 20, 2026
Merged

Support ?Sized types in Rng*: TryRng* blanket impls #51

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c14a054
Support `?Sized` types in `Rng*: TryRng*` blanket impls
tarcieri Jan 19, 2026
9966877
Add `RngCore` to `CryptoRng`'s bounds
tarcieri Jan 20, 2026
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9 changes: 6 additions & 3 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -59,7 +59,10 @@ pub trait RngCore: TryRngCore<Error = Infallible> {
fn fill_bytes(&mut self, dst: &mut [u8]);
}

impl<R: TryRngCore<Error = Infallible>> RngCore for R {
impl<R> RngCore for R
where
R: TryRngCore<Error = Infallible> + ?Sized,
{
#[inline]
fn next_u32(&mut self) -> u32 {
match self.try_next_u32() {
Expand All @@ -86,9 +89,9 @@ impl<R: TryRngCore<Error = Infallible>> RngCore for R {
///
/// This is a convenient trait alias for <code>[TryCryptoRng]<Error = [Infallible]></code>.
/// It is equivalent to the trait sum <code>[RngCore] + [TryCryptoRng]</code>.
pub trait CryptoRng: TryCryptoRng<Error = Infallible> {}
pub trait CryptoRng: RngCore + TryCryptoRng<Error = Infallible> {}
Comment on lines -89 to +92
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@dhardy dhardy Jan 20, 2026

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Interesting that this is necessary; it seems to indicate a trait solver issue.

But simple solutions are good!

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@tarcieri tarcieri Jan 23, 2026

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I think having explicit bounds even if they're covered by a blanket impl makes the compiler errors much better, because it will tell you explicitly why the bound wasn't satisfied, whereas figuring out why a blanket impl didn't work can be a lot of red herrings


impl<R: TryCryptoRng<Error = Infallible>> CryptoRng for R {}
impl<R> CryptoRng for R where R: TryCryptoRng<Error = Infallible> + ?Sized {}

/// Base trait for random number generators and random data sources
///
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