Why is Error a Box<ErrorKind>?

[Cobrand]

What makes the Box<_> necessary in the type Error = Box<ErrorKind> definition? As far as I've seen there is no mention of that either in the doc or in the code, and if I recall well it didn't use to have a Box<_> there.

[ZoeyR]

I can't find the issue where this was changed at the moment. But if I remember correctly is was an optimization because by boxing up the errors less bytes had to be put on the stack for returns.

[TyOverby]

@Cobrand: we ran performance tests and found that allocating a Box and copying the box around the stack was cheaper than copying the error value around the stack.

[Cobrand]

It used to be pretty simple to match all possibilities with one match, now without the (unstable) box pattern you have to use 2 match to get to the same result, that's why I asked why it changed.

Thanks for answering!

[TyOverby]

You should be able to use a single * to dereference and then you can match just like before