ehh i dunno

merge/box.go

@@ -44,14 +44,16 @@ func strip[X any](f func(X) error) func(interface{}) error {
 	}
 }
 
+func stripReturn[X any](f func() X) func() interface{} {
+	return func() interface {} { return f() }
+}
+
 // Box takes a mergeable value and creates a new mergeable value of type Boxed.
 // Any two Boxed values can attempt to merge at runtime.
 func Box[X Merges[X]](x X) Boxed {
 	return Boxed{
 		val: x,
-		ident: func() interface{} {
+		ident: stripReturn(x.MergeIdentity),
-			return x.MergeIdentity()
-		},
 		merge: strip(x.Merge),
 	}
 }

merge/merge.go

@@ -18,6 +18,7 @@ package merge
 // Although the type B satisfies the interface Merges[*C], it does not satisfy
 // the constraint [X Merges[X]], which is what is used throughout this package.
 type Merges[X any] interface {
+	// MergeIdentity defines the identity for the merge function
 	MergeIdentity() X
 	Merge(X) error
 }

merge/merge_test.go

@@ -10,15 +10,13 @@ type additive struct {
 	total int
 }
 
-func (*additive) MergeIdentity() *additive {
-	return new(additive)
-}
-
 func (a *additive) Merge(b *additive) error {
 	a.total += b.total
 	return nil
 }
 
+func (*additive) MergeIdentity() *additive { return new(additive) }
+
 func add(n int) *additive {
 	return &additive{total: n}
 }
@@ -27,9 +25,7 @@ type multiplicative struct {
 	scale int
 }
 
-func (m *multiplicative) MergeIdentity() *multiplicative {
+func (*multiplicative) MergeIdentity() *multiplicative { return &multiplicative{scale: 1} }
-	return &multiplicative{scale: 1}
-}
 
 func (m *multiplicative) Merge(v *multiplicative) error {
 	m.scale *= v.scale
@@ -46,14 +42,14 @@ type exclusive struct {
 	stock int
 }
 
-func (*exclusive) MergeIdentity() *exclusive { return new(exclusive) }
-
 func (e *exclusive) Merge(source *exclusive) error {
 	e.stock += source.stock
 	source.stock = 0
 	return nil
 }
 
+func (*exclusive) MergeIdentity() *exclusive { return new(exclusive) }
+
 func ex(n int) *exclusive {
 	return &exclusive{stock: n}
 }