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Raising custom error types/ const errors #160
Description
The io package declares an EOF error like this:
var EOF = errors.New("EOF")
using this pattern to raise custom errors leads to ugly stack traces since the errors are generated during intialization, not when they happen:
github.com/andig/gosml.init
/Users/andig/Documents/htdocs/go/src/github.com/andig/gosml/crc16.go:32
main.init
<autogenerated>:1
runtime.main
/usr/local/opt/go/libexec/src/runtime/proc.go:186
runtime.goexit
/usr/local/opt/go/libexec/src/runtime/asm_amd64.s:2361
in fact, the entire call stack of where is error happens is lost which means using the error type is impossible.
How could one implement custom error types or errors the can be behaviour-checked according to your blog article?
Activity
CreatCodeBuild commentedon Jun 18, 2018
you can always wrap it again
puellanivis commentedon Jun 18, 2018
https://dave.cheney.net/2016/04/07/constant-errors
Which contains, "Although, you really shouldn’t be using sentinel errors anyway."
davecheney commentedon Jun 18, 2018
andig commentedon Jun 19, 2018
Understood and thank you for your blog posts.
That works but still doesn't deliver and entirely "clean" stack trace as I'd desire.
Bottom line- with my limited go experience- seems to be that you cannot test wrapped (top-level) errors for behaviour (need to use causer instead) and stack traces will contain both inner error creation plus wrapping when "throwing" for that reason.
davecheney commentedon Jun 19, 2018
puellanivis commentedon Jun 19, 2018
Indeed, I recall in a previous bug/feature discussion, I suggested making a nicer Sentinel const-compatible type, and the recommendation was, “if we make it easier, people will use it, and we would like to actually discourage it.“
But regardless, a “good sentinel” value can be had with just a few lines of code. Sure the type ends up being unique to your package, (and hopefully actually unexported) but these are parts of what should hopefully make sentinel errors better than
var EOF = errors.New("EOF")with all the pitfalls of being able to then monkey around with the sentinel.As a note, the stdlib errors is not const-compatible, so. 😐
davecheney commentedon Oct 8, 2018
I'm sorry I haven't replied before now.
I'm going to close this issue as there is nothing to do here; this package isn't what you what, its designed in a way that is incompatible with your requirements.
Switch to runtime.CallersFrames
Switch to runtime.CallersFrames (#183)