add AsType helper fn

Author: Sypheos

cause_go118.go

@@ -2,6 +2,8 @@
 
 package errors
 
+import "errors"
+
 func IsOfType[T error](err error) bool {
 	for {
 		if _, ok := err.(T); ok || err == nil {
@@ -11,3 +13,9 @@ func IsOfType[T error](err error) bool {
 		err = Unwrap(err)
 	}
 }
+
+func AsType[T error](err error) (T, bool) {
+	var e T
+
+	return e, errors.As(err, &e)
+}

cause_go118_test.go

@@ -39,3 +39,35 @@ func TestIsOfType(t *testing.T) {
 		assert.Equal(t, tt.isMockError, IsOfType[mockError](tt.input))
 	}
 }
+
+func TestAsOfType(t *testing.T) {
+	for _, tt := range []struct {
+		name     string
+		input    error
+		expected error
+	}{
+		{
+			name: "nil error",
+		},
+		{
+			name:     "mockError",
+			input:    mockError{},
+			expected: mockError{},
+		},
+		{
+			name:     "wrapped mockError",
+			input:    Wrap(mockError{}, "wrapping"),
+			expected: mockError{},
+		},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			m, ok := AsType[mockError](tt.input)
+
+			assert.Equal(t, tt.expected != nil, ok)
+
+			if ok {
+				assert.Equal(t, tt.expected, m)
+			}
+		})
+	}
+}