feat(ptr): add RefOrNil

ptr/ptr.go

@@ -1,15 +1,20 @@
 package ptr
 
-import "github.com/go-board/std/cmp"
+import (
+	"github.com/go-board/std/cmp"
+)
 
 func zero[T any]() (v T) { return }
 
 // Ref return reference of value
 func Ref[T any](t T) *T { return &t }
 
-// Default return default value of type
-func Default[T any]() *T {
-	return Ref(zero[T]())
+// RefOrNil return reference of value if it not the zero value, else return nil
+func RefOrNil[T comparable](t T) *T {
+	if t == zero[T]() {
+		return nil
+	}
+	return &t
 }
 
 // ValueOr return value of pointer if not nil, else return default value.
@@ -28,8 +33,12 @@ func ValueOrZero[T any](v *T) T {
 // Compare compares two pointer. If both non-nil, compare underlying data,
 // if both nil, return 0, non-nil pointer is always greater than nil pointer.
 func Compare[T cmp.Ordered](l, r *T) int {
+	return CompareBy(l, r, cmp.Compare[T])
+}
+
+func CompareBy[T any](l, r *T, cmp func(T, T) int) int {
 	if l != nil && r != nil {
-		return cmp.Compare(*l, *r)
+		return cmp(*l, *r)
 	}
 	if l == nil && r == nil {
 		return 0
@@ -43,8 +52,12 @@ func Compare[T cmp.Ordered](l, r *T) int {
 // Equal test whether two pointer are equal. If both non-nil, test underlying data,
 // if both nil, return true, else return false
 func Equal[T comparable](l, r *T) bool {
+	return EqualBy(l, r, cmp.Equal[T])
+}
+
+func EqualBy[T any](l, r *T, eq func(T, T) bool) bool {
 	if l != nil && r != nil {
-		return *l == *r
+		return eq(*l, *r)
 	} else if l == nil && r == nil {
 		return true
 	}