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Remove unnecessary bounds on Error and Display implementations for TryLockError and PoisonError. #31589

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merged 1 commit into from
Feb 14, 2016
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Remove unnecessary bounds on Error and Display implementations for TryLockError and PoisonError. #31589

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11 changes: 7 additions & 4 deletions src/libstd/sys/common/poison.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -111,7 +111,7 @@ impl<T> fmt::Display for PoisonError<T> {
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Send + Reflect> Error for PoisonError<T> {
impl<T: Reflect> Error for PoisonError<T> {
fn description(&self) -> &str {
"poisoned lock: another task failed inside"
}
Expand Down Expand Up @@ -158,14 +158,17 @@ impl<T> fmt::Debug for TryLockError<T> {
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Send + Reflect> fmt::Display for TryLockError<T> {
impl<T> fmt::Display for TryLockError<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
self.description().fmt(f)
match *self {
TryLockError::Poisoned(..) => "poisoned lock: another task failed inside",
TryLockError::WouldBlock => "try_lock failed because the operation would block"
}.fmt(f)
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How come this can't continue to delegate to the same implementation? It seems unfortunate to have to duplicate this with description above

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Calling into the Error implementation via description would require adding a Reflect bound, which is not really needed here.

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But you can't have an instance of TryLockError<T> where T isn't Reflect, right?

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If you're dealing with a generic TryLockError<T> you would have to include the Reflect bound, which is annoying and impossible on stable, where you'd have to bound by Any, which is unnecessarily restrictive. You could do where TryLockError<T>: Display but this is also annoying if you have already asserted T: Display elsewhere.

EDIT: Actually under this definition you don't need any bounds on T, so that last line is wrong.

}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Send + Reflect> Error for TryLockError<T> {
impl<T: Reflect> Error for TryLockError<T> {
fn description(&self) -> &str {
match *self {
TryLockError::Poisoned(ref p) => p.description(),
Expand Down