Add routines to compare measurements against reference

[jraman567]

Adds a compare routine to some of the measurement types.

[jraman567]

I can't figure out the lint error; I'm unsure how to fix it.

[thomas-fossati]

I can't figure out the lint error; I'm unsure how to fix it.

I suggest giving a go at:

goimports -local "github.com/veraison/corim" -w .

[jraman567]

I suggest giving a go at:

goimports -local "github.com/veraison/corim" -w .

Thanks, @thomas-fossati; that helped to fix it. As Dionna suggested in the meeting, the fix needed a new line between "fmt" and the following line.

I'm working on the test coverage and will post a new revision of the changes shortly. Thank you!

[setrofim]

As a general note, it's weird for Compare() method to raise an error. Two values not being equal is not automatically considered an error condition. Also, I would expect a method called "Compare" to do a relative comparison, rather than equality test.

I would rename the method to Equal and have it return a bool instead.

(Alternatively, you could keep it as "Compare" and have it return an int, with 1 indicating o > r, -1 indicating r > o, and 0 indicating o == r; however, that would require chainging the implementations as well, and would require for all types in question to have partial ordering, which I don't think we want.)

[thomas-fossati]

Thanks, @thomas-fossati; that helped to fix it. As Dionna suggested in the meeting, the fix needed a new line between "fmt" and the following line.

Do you use vim or VS Code? If so, the popular go plugins (e.g., vim-go) should automatically update the import statements order transparently.

[thomas-fossati]

I agree with @setrofim high-level comment.

I think we should have:

• a Compare method for types for which ordering makes sense, e.g., SVNs -- and it should return -1,0,1 rather than error;
• an Equal method for types for which we are only concerned about strict equality (e.g., digests) -- and this could return a bool.

[setrofim]

an Equal method for types for which we are only concerned about strict equality (e.g., digests)

I think we should have Equal for the other types as well (even if it's just implemented as o.Compare(r) == 0), since that would allow you to handle of values uninformly as interface{ Equal() bool } in situatations where you only care about exact values.

[thomas-fossati]

an Equal method for types for which we are only concerned about strict equality (e.g., digests)

I think we should have Equal for the other types as well (even if it's just implemented as o.Compare(r) == 0), since that would allow you to handle of values uninformly as interface{ Equal() bool } in situatations where you only care about exact values.

WFM

[jraman567]

As a general note, it's weird for Compare() method to raise an error. Two values not being equal is not automatically considered an error condition. Also, I would expect a method called "Compare" to do a relative comparison, rather than equality test.

I also prefer a boolean return value. If we cannot perform the comparison due to an error, should we log it and return false for a result?

I would rename the method to Equal and have it return a bool instead.

It's not always equality; the type governs the semantics of comparison.

In the SVN type, for example, the comparison should be equality for the ExactValueType and greater-than-or-equal for MinValueType.

[jraman567]

OK, I'll push a PR with recommended changes. Thanks @thomas-fossati & @setrofim for the review.

[jraman567]

@thomas-fossati @setrofim could you please confirm if the PR looks good? Thanks!

[thomas-fossati]

Looks good, thanks @jraman567 !

There's one point to discuss about what to do with RawValue.