From 2aee4f1d83b9b156d77a33b444a2343409b3d5b6 Mon Sep 17 00:00:00 2001
From: Alexander Borsuk <me@alex.bio>
Date: Sun, 18 Feb 2024 15:02:47 +0200
Subject: [PATCH] Represent buffer vector as string_view

Signed-off-by: Alexander Borsuk <me@alex.bio>
---
 base/base_tests/buffer_vector_test.cpp | 35 +++++++++++++++++++++++++-
 base/buffer_vector.hpp                 |  9 +++++++
 2 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/base/base_tests/buffer_vector_test.cpp b/base/base_tests/buffer_vector_test.cpp
index 1abf1b8849..cde66d7ab1 100644
--- a/base/base_tests/buffer_vector_test.cpp
+++ b/base/base_tests/buffer_vector_test.cpp
@@ -21,7 +21,7 @@ namespace
 UNIT_TEST(BufferVector_PushBackAndRealloc)
 {
   using ElementT = std::vector<int>;
-  ElementT element({1, 2, 3});
+  ElementT const element({1, 2, 3});
 
   size_t constexpr kFixedSize = 2;
   {
@@ -414,3 +414,36 @@ UNIT_TEST(BufferVector_Erase)
       TEST_EQUAL(v1[i], v2[i], ());
   }
 }
+
+UNIT_TEST(BufferVector_StringView)
+{
+  {
+    buffer_vector<std::string_view::value_type, 4> bv = {'a', 'b', 'c', 'd'};
+    std::string_view constexpr svStack = "abcd";
+    TEST_EQUAL(svStack, std::string_view{bv}, ());
+
+    bv.push_back('e');
+    std::string_view constexpr svHeap = "abcde";
+    TEST_EQUAL(svHeap, std::string_view{bv}, ());
+  }
+
+  {
+    buffer_vector<std::u16string_view::value_type, 4> bv = {u'à', u'b', u'ç', u'ð'};
+    std::u16string_view constexpr svStack = u"àbçð";
+    TEST_EQUAL(svStack, std::u16string_view{bv}, ());
+
+    bv.push_back(u'ë');
+    std::u16string_view constexpr svHeap = u"àbçðë";
+    TEST_EQUAL(svHeap, std::u16string_view{bv}, ());
+  }
+
+  {
+    buffer_vector<std::u32string_view::value_type, 4> bv = {U'à', U'b', U'ç', U'ð'};
+    std::u32string_view constexpr svStack = U"àbçð";
+    TEST_EQUAL(svStack, std::u32string_view{bv}, ());
+
+    bv.push_back(U'ë');
+    std::u32string_view constexpr svHeap = U"àbçðë";
+    TEST_EQUAL(svHeap, std::u32string_view{bv}, ());
+  }
+}
diff --git a/base/buffer_vector.hpp b/base/buffer_vector.hpp
index 7d65879546..b5b32b0ac4 100644
--- a/base/buffer_vector.hpp
+++ b/base/buffer_vector.hpp
@@ -213,6 +213,11 @@ public:
     SetStaticSize(0);
   }
 
+  explicit operator std::basic_string_view<T> const()
+  {
+    return std::basic_string_view<T>{data(), size()};
+  }
+
   /// @todo Here is some inconsistencies:
   /// - "data" method should return 0 if vector is empty;\n
   /// - potential memory overrun if m_dynamic is empty;\n
@@ -288,6 +293,10 @@ public:
   }
 
   /// By value to be consistent with m_vec.push_back(m_vec[0]).
+  /// The bug comes after the following sequence:
+  /// 1. operator[] returns a reference for zero element.
+  /// 2. push_back causes switching from the stack to heap allocation and moves all elements (including zero one).
+  /// 3. An outdated reference to the already moved zero element is pushed back in the push_back.
   void push_back(T t)
   {
     if (!IsDynamic())
-- 
2.45.3