Using go1.18 and adding some interface types that can be used for generics

Makefile

@@ -1,4 +1,5 @@
-TEST := go test
+GO ?= go
+TEST := $(GO) test
 TEST_FLAGS ?= -v
 TEST_TARGET ?= .
 GO111MODULE = on

activity.go

@@ -199,6 +199,10 @@ type HasRecipients interface {
 	Clean()
 }
 
+type Activities interface {
+	Activity
+}
+
 // Activity is a subtype of Object that describes some form of action that may happen,
 // is currently happening, or has already happened.
 // The Activity type itself serves as an abstract base type for all types of activities.

actor.go

@@ -36,6 +36,10 @@ var ActorTypes = ActivityVocabularyTypes{
 // Like other ActivityStreams objects, actors have an id, which is a URI.
 type CanReceiveActivities Item
 
+type Actors interface {
+	Actor
+}
+
 // Actor is generally one of the ActivityStreams actor Types, but they don't have to be.
 // For example, a Profile object might be used as an actor, or a type from an ActivityStreams extension.
 // Actors are retrieved like any other Object in ActivityPub.

collection.go

@@ -21,6 +21,10 @@ var CollectionTypes = ActivityVocabularyTypes{
 	OrderedCollectionPageType,
 }
 
+type Collections interface {
+	Collection | CollectionPage | OrderedCollection | OrderedCollectionPage | ItemCollection
+}
+
 type CollectionInterface interface {
 	ObjectOrLink
 	Collection() ItemCollection

go.mod

@@ -1,6 +1,6 @@
 module github.com/go-ap/activitypub
 
-go 1.13
+go 1.18
 
 require (
 	git.sr.ht/~mariusor/go-xsd-duration v0.0.0-20200411073322-f0bcc40f0bf2

intransitive_activity.go

@@ -11,6 +11,10 @@ import (
 	"github.com/valyala/fastjson"
 )
 
+type IntransitiveActivities interface {
+	IntransitiveActivity | Question
+}
+
 // IntransitiveActivity Instances of IntransitiveActivity are a subtype of Activity representing intransitive actions.
 // The object property is therefore inappropriate for these activities.
 type IntransitiveActivity struct {

link.go

@@ -12,6 +12,10 @@ var LinkTypes = ActivityVocabularyTypes{
 	MentionType,
 }
 
+type Links interface {
+	Link | IRI
+}
+
 // A Link is an indirect, qualified reference to a resource identified by a URL.
 // The fundamental model for links is established by [ RFC5988].
 // Many of the properties defined by the Activity Vocabulary allow values that are either instances of APObject or Link.

object.go

@@ -133,6 +133,14 @@ func (a ActivityVocabularyType) MarshalBinary() ([]byte, error) {
 	return a.GobEncode()
 }
 
+type Objects interface {
+	Object | Tombstone | Place | Profile | Relationship |
+	Activities |
+	IntransitiveActivities |
+	Collections |
+	IRI
+}
+
 // Object describes an ActivityPub object of any kind.
 // It serves as the base type for most of the other kinds of objects defined in the Activity
 // Vocabulary, including other Core types such as Activity, IntransitiveActivity, Collection and OrderedCollection.
@@ -203,7 +211,7 @@ type Object struct {
 	// Updated the date and time at which the object was updated
 	Updated time.Time `jsonld:"updated,omitempty"`
 	// URL identifies one or more links to representations of the object
-	URL Item `jsonld:"url,omitempty"`
+	URL LinkOrIRI `jsonld:"url,omitempty"`
 	// To identifies an entity considered to be part of the public primary audience of an Activity Pub Object
 	To ItemCollection `jsonld:"to,omitempty"`
 	// Bto identifies anActivity Pub Object that is part of the private primary audience of this Activity Pub Object.