Drop the Sized constraint on impl Error for Box<T>
#39792
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Because of the implicit `Sized` constraint, `Box<Error>` does not implement `Error`, which is potentially surprising when trying to pass to a type which requires `T: Error`.
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r? @BurntSushi (rust_highfive has picked a reviewer for you, use r? to override) |
sgrif
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This was always a fairly clunky API. Its main upside was that type inference was able to figure out the error type in more cases than the current implementation does. It has much larger downsides though. The most common case is that you're just returning `diesel::result::Error` anyway, so this enum was just an annoyance. If you weren't returning that, you were probably returning an application specific error which has a variant for `diesel::result::Error`, and now also had to handle this additional type. It also turns out that [`TransactionError<Box<::std::error::Error>>` doesn't implement `::std::error::Error`](rust-lang/rust#39792). The new API might require explicitly stating the error type in a few more places (in particular `try!(conn.transaction(|| try!(query); Ok(()))); Ok(...)` stopped inferring), but I think that this will end up being more ergonomic for most uses.
sgrif
added a commit
to diesel-rs/diesel
that referenced
this pull request
Feb 13, 2017
This was always a fairly clunky API. Its main upside was that type inference was able to figure out the error type in more cases than the current implementation does. It has much larger downsides though. The most common case is that you're just returning `diesel::result::Error` anyway, so this enum was just an annoyance. If you weren't returning that, you were probably returning an application specific error which has a variant for `diesel::result::Error`, and now also had to handle this additional type. It also turns out that [`TransactionError<Box<::std::error::Error>>` doesn't implement `::std::error::Error`](rust-lang/rust#39792). The new API might require explicitly stating the error type in a few more places (in particular `try!(conn.transaction(|| try!(query); Ok(()))); Ok(...)` stopped inferring), but I think that this will end up being more ergonomic for most uses.
sgrif
added a commit
to diesel-rs/diesel
that referenced
this pull request
Feb 13, 2017
This was always a fairly clunky API. Its main upside was that type inference was able to figure out the error type in more cases than the current implementation does. It has much larger downsides though. The most common case is that you're just returning `diesel::result::Error` anyway, so this enum was just an annoyance. If you weren't returning that, you were probably returning an application specific error which has a variant for `diesel::result::Error`, and now also had to handle this additional type. It also turns out that [`TransactionError<Box<::std::error::Error>>` doesn't implement `::std::error::Error`](rust-lang/rust#39792). The new API might require explicitly stating the error type in a few more places (in particular `try!(conn.transaction(|| try!(query); Ok(()))); Ok(...)` stopped inferring), but I think that this will end up being more ergonomic for most uses.
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I believe the coherence error is why we can't do this :( |
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Wanna try it out? :) I vaguely remember this being a rabbit hole, but if travis is green and we can add this, then seems good to me. |
This attempts to address the coherence issues raised by 42e4007
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Hm. It didn't help. I don't see an obvious reason why (maybe something to do with |
sgrif
added a commit
to diesel-rs/diesel
that referenced
this pull request
Feb 13, 2017
This was always a fairly clunky API. Its main upside was that type inference was able to figure out the error type in more cases than the current implementation does. It has much larger downsides though. The most common case is that you're just returning `diesel::result::Error` anyway, so this enum was just an annoyance. If you weren't returning that, you were probably returning an application specific error which has a variant for `diesel::result::Error`, and now also had to handle this additional type. It also turns out that [`TransactionError<Box<::std::error::Error>>` doesn't implement `::std::error::Error`](rust-lang/rust#39792). The new API might require explicitly stating the error type in a few more places (in particular `try!(conn.transaction(|| try!(query); Ok(()))); Ok(...)` stopped inferring), but I think that this will end up being more ergonomic for most uses.
sgrif
added a commit
to diesel-rs/diesel
that referenced
this pull request
Feb 14, 2017
This was always a fairly clunky API. Its main upside was that type inference was able to figure out the error type in more cases than the current implementation does. It has much larger downsides though. The most common case is that you're just returning `diesel::result::Error` anyway, so this enum was just an annoyance. If you weren't returning that, you were probably returning an application specific error which has a variant for `diesel::result::Error`, and now also had to handle this additional type. It also turns out that [`TransactionError<Box<::std::error::Error>>` doesn't implement `::std::error::Error`](rust-lang/rust#39792). The new API might require explicitly stating the error type in a few more places (in particular `try!(conn.transaction(|| try!(query); Ok(()))); Ok(...)` stopped inferring), but I think that this will end up being more ergonomic for most uses.
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Because of the implicit
Sizedconstraint,Box<Error>does notimplement
Error, which is potentially surprising when trying to passto a type which requires
T: Error.