Diff Complex Data Structures? (structs, maps, slices, etc.)

[Felix Geisendoerfer]

I'm looking for a pkg that would allow me to compare nested data structures (e.g. a struct that has a field which is a slice of pointers to another struct, etc.) and produce a human readable output highlighting the difference between the two inputs. [1]

This would be super handy for some of the unit testing I'm trying to do. So far I'm using reflect.DeepEqual() which does the job, but it's really painful to debug if the comparison fails.

Many thanks in advance!

Cheers,

Felix

[Patrick Mézard]

We use a combination of go-spew ( https://github.com/davecgh/go-spew ), a regexp to drop pointers from go-spew output and go-difflib ( https://github.com/pmezard/go-difflib ) .

--
Patrick​

[Felix Geisendoerfer]

On Wednesday, June 25, 2014 1:59:40 PM UTC+2, patrick wrote:

We use a combination of go-spew ( https://github.com/davecgh/go-spew ), a regexp to drop pointers from go-spew output and go-difflib ( https://github.com/pmezard/go-difflib ) .

Good idea. Ideally this could be done without the regexp part. I've created an issue on the spew pkg [1]. Hopefully the author will agree to a Dump() variant that doesn't print pointer addresses. I'll try to release a pkg that integrates spew+difflib once I get this sorted.

Cheers,

Felix

[1] https://github.com/davecgh/go-spew/issues/18

[Keith Rarick]

> I'm looking for a pkg that would allow me to compare nested data structures

I attempted something like this with
http://godoc.org/github.com/kr/pretty#Diff
http://godoc.org/github.com/kr/pretty#Fdiff

It is good enough to be sometimes useful in tests and debugging,
but definitely far from complete.

[roger peppe]

The textual diff approach is interesting - I'd thought of doing
something more data-aware, but that's nice and generic.
It won't necessarily tell you what field the difference is found in though.

We currently use a different approach, which doesn't
give such complete results, but is useful in many cases.

See http://godoc.org/github.com/juju/testing/checkers#DeepEqual

It returns an error that describes where the deep-equal comparison fails
(it also compares a nil slice equal to an empty slice, which
is almost always what we want, because for testing purposes
we almost never want to distinguish the two)

The place it falls down is when you've got two long
slices that differ only in length. Perhaps a hybrid
approach could work well here - when there's a length
mismatch, resort to textual diff.

cheers,
rog.

[Felix Geisendörfer]

Thanks for the additional suggestions, I'll experiment with these next week and report back.

[Alfonso Vega-Garcia]

https://github.com/kylelemons/godebug
works pretty well.


-- Alfonso

Alfonso Vega-Garcia | Software Engineer | vegacom at gmail.com

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