Reporter - embedded types about go-cmp HOT 6 CLOSED

I apologize, but I don't understand what you're trying to do. Do you have an example?

from go-cmp.

Sorry I needed more coffee before I created this issue.

What I'm trying to do is create an audit history of user modifications to a business entity (represented by a struct). So after I saw the support for custom reporters in cmp.Diff I thought I'd compare the modified and original instances of the struct, and use a custom reporter to create the list of changes.

However I also don't want to expose the presence of any embedded types in the reported paths, so the path to each change matches the field location when serialised to JSON.

In code what I'm trying to do is something like this :

type Name struct {
	FirstName string
	LastName string
}

type Human struct {
	Name
	Age int
}

Alice := Human{
	Age: 31,
	Name: Name{
		FirstName:"Alice",
		LastName: "Example",
	},
}

// Alice's evil twin
Malice := Human{
	Age: 31,
	Name: Name{
		FirstName:"Malice",
		LastName: "Example",
	},
}

cmp.Diff(Alice, Malice, cmp.Reporter(exampleReporter))

// currently in PushStep(PathStep) when the reporter visits the "Name" field and I have to
// append that to the field path, and I end up with:
// {
//   {
//     Path : "Name.FirstName"
//     ...
//   },
// }

// But if I knew the field in the PathStep was an embedded type field I could skip that PathStep, and get :
// {
//   {
//     Path : "FirstName"
//     ...
//   },
// }

from go-cmp.

I see. For this use case, I don't think any modification is necessary.

I have a forked implementation that copies the value of the Anonymous from reflect.StructField to cmp.StructField in the compareStruct and that seems to do the job with minimal modification.

Given the cmp.Path where the nth step is a cmp.StructField, you can obtain the original reflect.StructField from the type information held in the n-1th step.

Specifically:

var p cmp.Path = ...
f, _ := p[n-1].Type().FieldByName(p[n].Name())

From that reflect.StructField you can interrogate whether Anonymous was set or not.

from go-cmp.

Also, since Reporter doesn't provide you a Path, you can trivially re-construct it by push/popping the provided PathSteps. See the example.

from go-cmp.

Thanks for the fast replies! And for taking the time to point me in the right direction, I'll give it a go.

from go-cmp.

Glad it helped, I'm going to close this as resolved. Feel free to respond if you need more assistance.

from go-cmp.