fix: FromNillable

Converts receiver method to constructor method.

option.go

@@ -56,6 +56,14 @@ func None[T any]() Option[T] {
 	return map[bool]T{}
 }
 
+// FromNillable converts a nillable value to an Option.
+func FromNillable[T any](v *T) Option[T] {
+	if v == nil {
+		return None[T]()
+	}
+	return Some(*v)
+}
+
 // IsSome returns whether the Option has a value or not.
 func (o Option[T]) IsSome() bool {
 	return len(o) != 0
@@ -234,11 +242,3 @@ func (o *Option[T]) UnmarshalJSON(data []byte) error {
 	*o = Some(v)
 	return nil
 }
-
-// FromNillable converts a nillable value to an Option.
-func (o Option[T]) FromNillable(v *T) Option[T] {
-	if v == nil {
-		return None[T]()
-	}
-	return Some(*v)
-}

option_test.go

@@ -8,7 +8,7 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/assert"
-	"github.com/tapp-ai/go-optional-v2"
+	optionalv2 "github.com/tapp-ai/go-optional-v2"
 )
 
 // Custom type for testing fmt.Stringer interface
@@ -34,6 +34,20 @@ func TestOption(t *testing.T) {
 		assert.True(t, optNone.IsNone())
 	})
 
+	// Test FromNillable method
+	t.Run("FromNillable", func(t *testing.T) {
+		var value *int = nil
+		opt := optionalv2.FromNillable(value)
+		assert.False(t, opt.IsSome())
+		assert.True(t, opt.IsNone())
+
+		value = new(int)
+		*value = 42
+		opt = optionalv2.FromNillable(value)
+		assert.True(t, opt.IsSome())
+		assert.Equal(t, 42, opt.Unwrap())
+	})
+
 	// Test Unwrap and UnwrapAsPtr methods
 	t.Run("UnwrapMethods", func(t *testing.T) {
 		optSome := optionalv2.Some("Hello")