BLI: new StringRef and StringRefNull data structures

These two data structures reference strings somewhere in memory.
They do not own the referenced string. The string is considered
const.

A string referenced by StringRefNull can be expected to be
null-terminated. That is not the case for StringRef.

This commit is a continuation of rB369d5e8ad2bb7c2.

2 files changed, 245 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_string_ref.h b/source/blender/blenlib/BLI_string_ref.h
new file mode 100644
index 00000000000..9d4678f335f
--- /dev/null
+++ b/source/blender/blenlib/BLI_string_ref.h
@@ -0,0 +1,244 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+/** \file
+ * \ingroup bli
+ *
+ * A StringRef is a pointer to a string somewhere in memory. It should not be used to transfer
+ * ownership of that string. When a function gets a StringRef as input, it cannot expect, that
+ * the string will still exist after the function ends.
+ *
+ * There are two types of string references: One that guarantees null termination and one that does
+ * not.
+ */
+
+#pragma once
+
+#include <cstring>
+#include <string>
+#include <sstream>
+
+#include "BLI_utildefines.h"
+#include "BLI_array_ref.h"
+
+namespace BLI {
+
+class StringRef;
+
+class StringRefBase {
+ public:
+  using size_type = size_t;
+
+ protected:
+  const char *m_data;
+  size_type m_size;
+
+  StringRefBase(const char *data, size_type size) : m_data(data), m_size(size)
+  {
+  }
+
+ public:
+  /**
+   * Return the (byte-)length of the referenced string, without any null-terminator.
+   */
+  size_type size() const
+  {
+    return m_size;
+  }
+
+  /**
+   * Return a pointer to the start of the string.
+   */
+  const char *data() const
+  {
+    return m_data;
+  }
+
+  char operator[](size_type index) const
+  {
+    BLI_assert(index <= m_size);
+    return m_data[index];
+  }
+
+  operator ArrayRef<char>() const
+  {
+    return ArrayRef<char>(m_data, m_size);
+  }
+
+  operator std::string() const
+  {
+    return std::string(m_data, m_size);
+  }
+
+  const char *begin() const
+  {
+    return m_data;
+  }
+
+  const char *end() const
+  {
+    return m_data + m_size;
+  }
+
+  void copy_to__with_null(char *dst) const
+  {
+    memcpy(dst, m_data, m_size);
+    dst[m_size] = '\0';
+  }
+
+  /**
+   * Returns true when the string begins with the given prefix. Otherwise false.
+   */
+  bool startswith(StringRef prefix) const;
+
+  /**
+   * Returns true when the string ends with the given suffix. Otherwise false.
+   */
+  bool endswith(StringRef suffix) const;
+};
+
+/**
+ * References a null-terminated char array.
+ */
+class StringRefNull : public StringRefBase {
+
+ public:
+  StringRefNull() : StringRefBase("", 0)
+  {
+  }
+
+  StringRefNull(const char *str) : StringRefBase(str, strlen(str))
+  {
+    BLI_assert(str != NULL);
+    BLI_assert(m_data[m_size] == '\0');
+  }
+
+  StringRefNull(const char *str, size_type size) : StringRefBase(str, size)
+  {
+    BLI_assert(str[size] == '\0');
+  }
+
+  StringRefNull(const std::string &str) : StringRefNull(str.data())
+  {
+  }
+};
+
+/**
+ * References a char array. It might not be null terminated.
+ */
+class StringRef : public StringRefBase {
+ public:
+  StringRef() : StringRefBase(nullptr, 0)
+  {
+  }
+
+  StringRef(StringRefNull other) : StringRefBase(other.data(), other.size())
+  {
+  }
+
+  StringRef(const char *str) : StringRefBase(str, str ? strlen(str) : 0)
+  {
+  }
+
+  StringRef(const char *str, size_type length) : StringRefBase(str, length)
+  {
+  }
+
+  StringRef(const std::string &str) : StringRefBase(str.data(), str.size())
+  {
+  }
+
+  /**
+   * Return a new StringRef that does not contain the first n chars.
+   */
+  StringRef drop_prefix(uint n) const
+  {
+    BLI_assert(n <= m_size);
+    return StringRef(m_data + n, m_size - n);
+  }
+
+  /**
+   * Return a new StringRef that with the given prefix being skipped.
+   * Asserts that the string begins with the given prefix.
+   */
+  StringRef drop_prefix(StringRef prefix) const
+  {
+    BLI_assert(this->startswith(prefix));
+    return this->drop_prefix(prefix.size());
+  }
+};
+
+/* More inline functions
+ ***************************************/
+
+inline std::ostream &operator<<(std::ostream &stream, StringRef ref)
+{
+  stream << std::string(ref);
+  return stream;
+}
+
+inline std::ostream &operator<<(std::ostream &stream, StringRefNull ref)
+{
+  stream << std::string(ref.data(), ref.size());
+  return stream;
+}
+
+inline std::string operator+(StringRef a, StringRef b)
+{
+  return std::string(a) + std::string(b);
+}
+
+inline bool operator==(StringRef a, StringRef b)
+{
+  if (a.size() != b.size()) {
+    return false;
+  }
+  return STREQLEN(a.data(), b.data(), a.size());
+}
+
+inline bool operator!=(StringRef a, StringRef b)
+{
+  return !(a == b);
+}
+
+inline bool StringRefBase::startswith(StringRef prefix) const
+{
+  if (m_size < prefix.m_size) {
+    return false;
+  }
+  for (uint i = 0; i < prefix.m_size; i++) {
+    if (m_data[i] != prefix.m_data[i]) {
+      return false;
+    }
+  }
+  return true;
+}
+
+inline bool StringRefBase::endswith(StringRef suffix) const
+{
+  if (m_size < suffix.m_size) {
+    return false;
+  }
+  uint offset = m_size - suffix.m_size;
+  for (uint i = 0; i < suffix.m_size; i++) {
+    if (m_data[offset + i] != suffix.m_data[i]) {
+      return false;
+    }
+  }
+  return true;
+}
+
+}  // namespace BLI
diff --git a/source/blender/blenlib/CMakeLists.txt b/source/blender/blenlib/CMakeLists.txt
index b4db305ccd4..abef583913c 100644
--- a/source/blender/blenlib/CMakeLists.txt
+++ b/source/blender/blenlib/CMakeLists.txt
@@ -225,6 +225,7 @@ set(SRC
   BLI_strict_flags.h
   BLI_string.h
   BLI_string_cursor_utf8.h
+  BLI_string_ref.h
   BLI_string_utf8.h
   BLI_string_utils.h
   BLI_sys_types.h