From b1b1981ae525ca54711dd49ff7833c1467b26afa Mon Sep 17 00:00:00 2001
From: Wojciech Nagrodzki <278594+wnagrodzki@users.noreply.github.com>
Date: Sat, 30 Mar 2019 08:45:05 +0100
Subject: [PATCH] Added "Avoid specifying access control modifiers on extension
 level" section

---
 README.md | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/README.md b/README.md
index e08fde8..f9f496f 100644
--- a/README.md
+++ b/README.md
@@ -91,6 +91,32 @@ Gather IBOutlets in one group above all the other properties and keep them priva
 
 > Outlets are implementation detail and should be kept private. Gathering them in one grup above all the other properties is old convention.
 
+### Avoid specifying access control modifiers on extension level
+
+Access control modifiers should not be specified on extension level:
+
+```swift
+private extension MyType {
+    func method() {
+        // code using helper()
+    }
+    func helper() { ... }
+}
+```
+
+But on member level:
+
+```swift
+extension MyType {
+    fileprivate func method() {
+        // code using helper()
+    }
+    private func helper() { ... }
+}
+```
+
+> This is to introduce distinction between members that should be visible from different types in the same file and those which should not. (`private extension` has the same result as `fileprivate extension` where all members end up being `fileprivate`).
+
 ### Avoid double negation
 
 Don't not avoid double negation.