Suggestion: Add comparator for structs

[ScreamingHawk]

What is considered comparable in Go?

• Structs if all of their fields are also comparable independently

Would be great to be able to pass a key (or function) to for struct comparison instead of relying on complete field equality.

Particularly useful when comparing structs with incomplete data (e.g. from an API) with complete data (e.g. from DB).

[deckarep]

Hello,

Thanks for the recommendation! I'm certainly not opposed to changes that would be considered general enough that others would find useful and if you have an API in mind I'd love to hear more details.

This package is so widely used it would be help to get more context and allow others to chime in.

[ScreamingHawk]

Here's some pseudo code for the pattern I've got. Please forgive errors.

type Entity struct {
  ID        uint64
  Data1 string
  Data2 bool
  // ...
  UpdatedAt *time.Time
}

func Update(apiEntities []*Entity) error {
  dbEntities = db.ListEntities()
  origSet := mapset.NewSet(dbEntities...)
  updateSet := mapset.NewSet(apiEntities...)

  added := updateSet.Difference(origSet)
  // Process newly added entries

  removed := origSet.Difference(updateSet)
  // Process deleted entries
}

Entity's that come in via the API don't have an ID populated, this causes all data to not match.
Also in this case UpdatedAt should be ignored when looking for equality.

If we could pass a function to do the comparison, that would be a nice general solution.
Something like:

func entityEqual(a Entity, b Entity) bool {
  // Whatever logic here
  return a.Data1 == b.Data1 && a.Data2 == b.Data2
}

func Update(apiEntities []*Entity) error {
  // ...
  added := updateSet.Difference(origSet, entityEqual)
  // ...
}

[deckarep]

Sounds good I’ll be looking at this next week due to a new project deadline so please forgive the upcoming delay!

…

On Wed, Jul 10, 2024 at 4:01 PM Michael Standen ***@***.***> wrote: Here's some pseudo code for the pattern I've got. Please forgive errors. type Entity struct { ID uint64 Data1 string Data2 bool // ... UpdatedAt *time.Time } func Update(apiEntities []*Entity) error { dbEntities = db.ListEntities() origSet := mapset.NewSet(dbEntities...) updateSet := mapset.NewSet(apiEntities...) added := updateSet.Difference(origSet) // Process newly added entries removed := origSet.Difference(updateSet) // Process deleted entries } Entity's that come in via the API don't have an ID populated, this causes all data to not match. Also in this case UpdatedAt should be ignored when looking for equality. If we could pass a function to do the comparison, that would be a nice general solution. Something like: func entityEqual(a Entity, b Entity) bool { // Whatever logic here return a.Data1 == b.Data1 && a.Data2 == b.Data2 } func Update(apiEntities []*Entity) error { // ... added := updateSet.Difference(origSet, entityEqual) // ... } — Reply to this email directly, view it on GitHub <#139 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AABQ73R6UMVPORVJYVXZG23ZLW4NTAVCNFSM6AAAAABKVWYCHKVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDEMRRGY3DMMBSGM> . You are receiving this because you commented.Message ID: ***@***.***>

[deckarep]

@ScreamingHawk - circling back on this seems like this would be a fairly large breaking change. I understand what your concern is but I do feel like this would possibly complicate the API. I'm still thinking about it.