From 790ee5daffad0518fec51092b89ca4ffcd3f237a Mon Sep 17 00:00:00 2001
From: Brendan Asselstine <mail.asselstine@gmail.com>
Date: Fri, 14 Aug 2020 16:15:38 -0700
Subject: [PATCH] Added initialize protection to MappedSinglyLinkedList

---
 contracts/test/MappedSinglyLinkedListExposed.sol | 2 +-
 contracts/utils/MappedSinglyLinkedList.sol       | 2 +-
 test/MappedSinglyLinkedListExposed.test.js       | 5 +++++
 3 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/contracts/test/MappedSinglyLinkedListExposed.sol b/contracts/test/MappedSinglyLinkedListExposed.sol
index 8c8878b9..899619cb 100644
--- a/contracts/test/MappedSinglyLinkedListExposed.sol
+++ b/contracts/test/MappedSinglyLinkedListExposed.sol
@@ -7,7 +7,7 @@ contract MappedSinglyLinkedListExposed {
 
   MappedSinglyLinkedList.Mapping list;
 
-  constructor () public {
+  function initialize() external {
     list.initialize();
   }
 
diff --git a/contracts/utils/MappedSinglyLinkedList.sol b/contracts/utils/MappedSinglyLinkedList.sol
index 59829b8c..d73498b1 100644
--- a/contracts/utils/MappedSinglyLinkedList.sol
+++ b/contracts/utils/MappedSinglyLinkedList.sol
@@ -19,8 +19,8 @@ library MappedSinglyLinkedList {
   /// @notice Initializes the list.
   /// @dev It is important that this is called so that the SENTINAL is correctly setup.
   function initialize(Mapping storage self) internal {
+    require(self.count == 0, "Already init");
     self.addressMap[SENTINAL] = SENTINAL;
-    self.count = 0;
   }
 
   function addAddresses(Mapping storage self, address[] memory addresses) internal {
diff --git a/test/MappedSinglyLinkedListExposed.test.js b/test/MappedSinglyLinkedListExposed.test.js
index e440ba3d..f04b5068 100644
--- a/test/MappedSinglyLinkedListExposed.test.js
+++ b/test/MappedSinglyLinkedListExposed.test.js
@@ -22,6 +22,7 @@ describe('MappedSinglyLinkedListExposed', function() {
     [wallet, wallet2, wallet3, wallet4] = await buidler.ethers.getSigners()
 
     list = await deployContract(wallet, MappedSinglyLinkedListExposed, [], overrides)
+    await list.initialize()
     await list.addAddresses([wallet2._address])
   })
 
@@ -29,6 +30,10 @@ describe('MappedSinglyLinkedListExposed', function() {
     it('should have initialized with a value', async () => {
       expect(await list.contains(wallet2._address)).to.be.true
     })
+
+    it('should not be initialized after it contains values', async () => {
+      await expect(list.initialize()).to.be.revertedWith('Already init')
+    })
   })
 
   describe('addressArray', () =>{