From 29ba8408181362420acb20bcad2a82f22e033d19 Mon Sep 17 00:00:00 2001
From: Adam Simpkins <simpkins@fb.com>
Date: Thu, 20 Feb 2014 15:28:50 -0800
Subject: [PATCH] add operator +, ==, and != to Cursor classes

Summary:
Add operator+, which returns a new Cursor pointing the specified number
of bytes ahead.  Cursor already implemented a += operator.

Also add == and != operators for checking to see if two cursors are
pointing to the same location.  Note that some derived cursor classes do
contain additional state, and we don't consider that state when
comparing for equality.  For instance, two Appenders pointing to the
same location will compare as equal, even if they are configured with
different growth parameters.  It seems like this is the behavior most
users will expect, but let me know if you have concerns about this.

Test Plan: Updated the unit tests to exercise the new operators.

Reviewed By: davejwatson@fb.com

FB internal diff: D1183537
---
 folly/io/Cursor.h                 | 18 ++++++++++++++++++
 folly/io/test/IOBufCursorTest.cpp | 18 +++++++++++++-----
 2 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/folly/io/Cursor.h b/folly/io/Cursor.h
index 764f52a1..f893d5a4 100644
--- a/folly/io/Cursor.h
+++ b/folly/io/Cursor.h
@@ -84,6 +84,24 @@ class CursorBase {
     p->skip(offset);
     return *p;
   }
+  Derived operator+(size_t offset) const {
+    Derived other(*this);
+    other.skip(offset);
+    return other;
+  }
+
+  /**
+   * Compare cursors for equality/inequality.
+   *
+   * Two cursors are equal if they are pointing to the same location in the
+   * same IOBuf chain.
+   */
+  bool operator==(const Derived& other) const {
+    return (offset_ == other.offset_) && (crtBuf_ == other.crtBuf_);
+  }
+  bool operator!=(const Derived& other) const {
+    return !operator==(other);
+  }
 
   template <class T>
   typename std::enable_if<std::is_arithmetic<T>::value, T>::type
diff --git a/folly/io/test/IOBufCursorTest.cpp b/folly/io/test/IOBufCursorTest.cpp
index e0bf5a5a..d0f369c3 100644
--- a/folly/io/test/IOBufCursorTest.cpp
+++ b/folly/io/test/IOBufCursorTest.cpp
@@ -98,15 +98,23 @@ TEST(IOBuf, copy_assign_convert) {
   EXPECT_EQ(3, cursor4.read<uint8_t>());
 }
 
-TEST(IOBuf, overloading) {
-  unique_ptr<IOBuf> iobuf1(IOBuf::create(20));
-  iobuf1->append(20);
-  RWPrivateCursor wcursor(iobuf1.get());
+TEST(IOBuf, arithmetic) {
+  IOBuf iobuf1(IOBuf::CREATE, 20);
+  iobuf1.append(20);
+  RWPrivateCursor wcursor(&iobuf1);
   wcursor += 1;
   wcursor.write((uint8_t)1);
-  Cursor cursor(iobuf1.get());
+  Cursor cursor(&iobuf1);
   cursor += 1;
   EXPECT_EQ(1, cursor.read<uint8_t>());
+
+  Cursor start(&iobuf1);
+  Cursor cursor2 = start + 9;
+  EXPECT_EQ(7, cursor2 - cursor);
+  EXPECT_NE(cursor, cursor2);
+  cursor += 8;
+  cursor2 = cursor2 + 1;
+  EXPECT_EQ(cursor, cursor2);
 }
 
 TEST(IOBuf, endian) {
-- 
2.34.1