From b6539a2639d86bb18cffe7383a9b0a25ede6a71f Mon Sep 17 00:00:00 2001
From: Ka Ho Ng <khng300@gmail.com>
Date: Fri, 19 Jan 2018 23:45:53 +0800
Subject: [PATCH] Add INVALID_ID as a constant for Id class Template

This is for identifying invalid ID from normal ID.
---
 src/indexer.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/indexer.h b/src/indexer.h
index 93f4e5ec..04315002 100644
--- a/src/indexer.h
+++ b/src/indexer.h
@@ -35,6 +35,8 @@ template <typename T>
 struct Id {
   size_t id;
 
+  static constexpr size_t INVALID_ID = static_cast<size_t>(-1);
+
   Id() : id(0) {}  // Needed for containers. Do not use directly.
   explicit Id(size_t id) : id(id) {}