We have gone a bit down a tangent here. My original complaint was about the friction of different error types compared to other languages (like, say, Go). Havi

We have gone a bit down a tangent here. My original complaint was about the friction of different error types compared to other languages (like, say, Go). Having to implement a bunch of From traits (unless you need io::Error, because everything seemed to have conversions from/to that), or having to implement inline error conversion through map_err, is such friction. I might go as far as consider it the most cumbersome error system I have used. Clean idea, cumbersome implementation. My comment about '?' not working with mismatched types was mostly just to say that it doesn't fix anything, it just adds a bit of convenient syntactic sugar.