Go2 Error Handling - Alternate Handler Concept

[Liam]

Re the Go2 Error Handling proposal

  https://go.googlesource.com/proposal/+/master/design/go2draft-error-handling.md

I have posted this feedback

  https://gist.github.com/networkimprov/c6cb3e2dff18d31840f2ef22e79d4a1e

Which contains an alternate handler concept. Please let me know if you think this merits its own github.com/golang issue.

A flag identifier indicates errors of various types. This also allows chaining of handlers with the same flag name. There are options for the #flag syntax, e.g. flag!, $flag, @flag, etc.

func f() {
   v, #ret := returnIfError()   // #ret can be any type; any non-zero value for it triggers its catch
   v, #fat := fatalIfError()    // #ret, etc are (probably) not local variables
   v, #wrt := writeOnError()
   if v != nice { // new scope
      #fat = MyError{msg:"!nice", ...}
      catch fat error { debug.PrintStack() }      // no return/exit; chained with next catch fat
   }
   #packageFlag = anotherError() // invokes package-level handler
   
   catch ret error { return ret }                 // if type is error, type name could be optional
   catch fat error { log.Fatal(fat) }
   catch wrt error { con.Write(...); return nil } // return/exit required in last handler on chain
}

catch packageFlag error { ... } // package-level handler; packageFlag is not a package variable

[Vlad Didenko]

Some time ago, after going through a very similar design (really, even had the catch clause in there), I have arrived at a more generalized version of it. That contemplation (still available at https://didenko.github.io/grab/grab_worth_it_0.1.1.html ) was very much unaccepted here.

Well, I actually do not remember if it was posted here or in golang-dev.

[Liam Breck]

Well, that was then, this is now...

I'll just note that 10 of 30 feedback posts on the error handling draft feedback wiki have asked for named handlers. Can I add your link there?

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[Vlad Didenko]

Absolutely, go ahead, thank you! I can add more "why" reasoning about "grab" design differences from "catch", but won't get to it until next weekend :(

[Liam Breck]

Posted your link to the feedback wiki, and to my design-revision draft, which will land on the issue tracker this week.

https://golang.org/wiki/Go2ErrorHandlingFeedback

https://gist.github.com/networkimprov/c6cb3e2dff18d31840f2ef22e79d4a1e