De-duplicate common code from StringPiece, StringPiece16, and their tests.

base/string_piece.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 // Copied from strings/stringpiece.h with modifications
 //
 // A string-like object that points to a sized piece of memory.
 //
 // Functions or methods may use const StringPiece& parameters to accept either
 // a "const char*" or a "string" value that will be implicitly converted to
 // a StringPiece.  The implicit conversion means that it is often appropriate
@@ skipping 15 matching lines @@
 
 #include <string>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/hash_tables.h"
 #include "base/string16.h"
 
 namespace base {
 
-class BASE_EXPORT StringPiece {
+template <typename STRING_TYPE> class BasicStringPiece;
+
+namespace internal {
+
+// Defines the types, methods, operators, and data members common to both
+// StringPiece and StringPiece16. Do not refer to this class directly, but
+// rather to BasicStringPiece, StringPiece, or StringPiece16.
+template <typename STRING_TYPE> class StringPieceDetail {
  public:
   // standard STL container boilerplate
   typedef size_t size_type;
-  typedef char value_type;
-  typedef const char* pointer;
-  typedef const char& reference;
-  typedef const char& const_reference;
+  typedef typename STRING_TYPE::value_type value_type;
+  typedef const value_type* pointer;
+  typedef const value_type& reference;
+  typedef const value_type& const_reference;
   typedef ptrdiff_t difference_type;
-  typedef const char* const_iterator;
-  typedef const char* iterator;
+  typedef const value_type* const_iterator;
   typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
-  typedef std::reverse_iterator<iterator> reverse_iterator;
 
   static const size_type npos;
 
  public:
   // We provide non-explicit singleton constructors so users can pass
   // in a "const char*" or a "string" wherever a "StringPiece" is
-  // expected.
-  StringPiece() : ptr_(NULL), length_(0) { }
-  StringPiece(const char* str)
-    : ptr_(str), length_((str == NULL) ? 0 : strlen(str)) { }
-  StringPiece(const std::string& str)
-    : ptr_(str.data()), length_(str.size()) { }
-  StringPiece(const char* offset, size_type len)
-    : ptr_(offset), length_(len) { }
+  // expected (likewise for char16, string16, StringPiece16).
+  StringPieceDetail() : ptr_(NULL), length_(0) {}
+  StringPieceDetail(const value_type* str)
+      : ptr_(str),
+      length_((str == NULL) ? 0 : STRING_TYPE::traits_type::length(str)) {}
+  StringPieceDetail(const STRING_TYPE& str)
+      : ptr_(str.data()),
+        length_(str.size()) {}
+  StringPieceDetail(const value_type* offset, size_type len)
+      : ptr_(offset),
+        length_(len) {}
 
   // data() may return a pointer to a buffer with embedded NULs, and the
   // returned buffer may or may not be null terminated.  Therefore it is
   // typically a mistake to pass data() to a routine that expects a NUL
   // terminated string.
-  const char* data() const { return ptr_; }
+  const value_type* data() const { return ptr_; }
   size_type size() const { return length_; }
   size_type length() const { return length_; }
   bool empty() const { return length_ == 0; }
 
   void clear() {
     ptr_ = NULL;
     length_ = 0;
   }
-  void set(const char* data, size_type len) {
+  void set(const value_type* data, size_type len) {
     ptr_ = data;
     length_ = len;
   }
-  void set(const char* str) {
+  void set(const value_type* str) {
     ptr_ = str;
-    length_ = str ? strlen(str) : 0;
-  }
-  void set(const void* data, size_type len) {
-    ptr_ = reinterpret_cast<const char*>(data);
-    length_ = len;
+    length_ = str ? STRING_TYPE::traits_type::length(str) : 0;
   }
 
-  char operator[](size_type i) const { return ptr_[i]; }
+  value_type operator[](size_type i) const { return ptr_[i]; }
 
   void remove_prefix(size_type n) {
     ptr_ += n;
     length_ -= n;
   }
 
   void remove_suffix(size_type n) {
     length_ -= n;
   }
 
-  int compare(const StringPiece& x) const {
+  int compare(const BasicStringPiece<STRING_TYPE>& x) const {
     int r = wordmemcmp(
         ptr_, x.ptr_, (length_ < x.length_ ? length_ : x.length_));
     if (r == 0) {
       if (length_ < x.length_) r = -1;
       else if (length_ > x.length_) r = +1;
     }
     return r;
   }
 
-  std::string as_string() const {
+  STRING_TYPE as_string() const {
     // std::string doesn't like to take a NULL pointer even with a 0 size.
-    return std::string(!empty() ? data() : "", size());
+    return empty() ? STRING_TYPE() : STRING_TYPE(data(), size());
   }
 
-  void CopyToString(std::string* target) const;
-  void AppendToString(std::string* target) const;
-
-  // Does "this" start with "x"
-  bool starts_with(const StringPiece& x) const {
-    return ((length_ >= x.length_) &&
-            (wordmemcmp(ptr_, x.ptr_, x.length_) == 0));
-  }
-
-  // Does "this" end with "x"
-  bool ends_with(const StringPiece& x) const {
-    return ((length_ >= x.length_) &&
-            (wordmemcmp(ptr_ + (length_-x.length_), x.ptr_, x.length_) == 0));
-  }
-
-  iterator begin() const { return ptr_; }
-  iterator end() const { return ptr_ + length_; }
+  const_iterator begin() const { return ptr_; }
+  const_iterator end() const { return ptr_ + length_; }
   const_reverse_iterator rbegin() const {
     return const_reverse_iterator(ptr_ + length_);
   }
   const_reverse_iterator rend() const {
     return const_reverse_iterator(ptr_);
   }
 
   size_type max_size() const { return length_; }
   size_type capacity() const { return length_; }
 
+  static int wordmemcmp(const value_type* p,
+                        const value_type* p2,
+                        size_type N) {
+    return STRING_TYPE::traits_type::compare(p, p2, N);
+  }
+
+ protected:
+  const value_type* ptr_;
+  size_type     length_;
+};
+
+template <typename STRING_TYPE>
+const typename StringPieceDetail<STRING_TYPE>::size_type
+StringPieceDetail<STRING_TYPE>::npos =
+    typename StringPieceDetail<STRING_TYPE>::size_type(-1);
+
+// MSVC doesn't like complex extern templates and DLLs.
+#if !defined(COMPILER_MSVC)
+extern template class BASE_EXPORT StringPieceDetail<std::string>;
+extern template class BASE_EXPORT StringPieceDetail<string16>;
+#endif
+
+}  // namespace internal
+
+// Defines the template type that is instantiated as either StringPiece or
+// StringPiece16.
+template <typename STRING_TYPE> class BasicStringPiece :
+    public internal::StringPieceDetail<STRING_TYPE> {
+ public:
+  typedef typename internal::StringPieceDetail<STRING_TYPE>::value_type
+      value_type;
+  typedef typename internal::StringPieceDetail<STRING_TYPE>::size_type
+      size_type;
+
+  BasicStringPiece() {}
+  BasicStringPiece(const value_type*str)
+      : internal::StringPieceDetail<STRING_TYPE>(str) {}
+  BasicStringPiece(const STRING_TYPE& str)
+      : internal::StringPieceDetail<STRING_TYPE>(str) {}
+  BasicStringPiece(const value_type* offset, size_type len)
+      : internal::StringPieceDetail<STRING_TYPE>(offset, len) {}
+};
+
+// Specializes BasicStringPiece for std::string to add a few operations that
+// are not needed for string16.
+template <> class BASE_EXPORT BasicStringPiece<std::string> :
+    public internal::StringPieceDetail<std::string> {
+ public:
+  BasicStringPiece() {}
+  BasicStringPiece(const char* str)
+      : internal::StringPieceDetail<std::string>(str) {}
+  BasicStringPiece(const std::string& str)
+      : internal::StringPieceDetail<std::string>(str) {}
+  BasicStringPiece(const char* offset, size_type len)
+      : internal::StringPieceDetail<std::string>(offset, len) {}
+
+  // Prevent the following overload of set() from hiding the definitions in the
+  // base class.
+  using internal::StringPieceDetail<std::string>::set;
+
+  void set(const void* data, size_type len) {
+    ptr_ = reinterpret_cast<const value_type*>(data);
+    length_ = len;
+  }
+
+  void CopyToString(std::string* target) const;
+  void AppendToString(std::string* target) const;
+
+  // Does "this" start with "x"
+  bool starts_with(const BasicStringPiece& x) const {
+    return ((length_ >= x.length_) &&
+            (wordmemcmp(ptr_, x.ptr_, x.length_) == 0));
+  }
+
+  // Does "this" end with "x"
+  bool ends_with(const BasicStringPiece& x) const {
+    return ((length_ >= x.length_) &&
+            (wordmemcmp(ptr_ + (length_-x.length_), x.ptr_, x.length_) == 0));
+  }
+
   size_type copy(char* buf, size_type n, size_type pos = 0) const;
 
-  size_type find(const StringPiece& s, size_type pos = 0) const;
+  size_type find(const BasicStringPiece& s, size_type pos = 0) const;
   size_type find(char c, size_type pos = 0) const;
-  size_type rfind(const StringPiece& s, size_type pos = npos) const;
+  size_type rfind(const BasicStringPiece& s, size_type pos = npos) const;
   size_type rfind(char c, size_type pos = npos) const;
 
-  size_type find_first_of(const StringPiece& s, size_type pos = 0) const;
+  size_type find_first_of(const BasicStringPiece& s, size_type pos = 0) const;
   size_type find_first_of(char c, size_type pos = 0) const {
     return find(c, pos);
   }
-  size_type find_first_not_of(const StringPiece& s, size_type pos = 0) const;
+  size_type find_first_not_of(const BasicStringPiece& s,
+                              size_type pos = 0) const;
   size_type find_first_not_of(char c, size_type pos = 0) const;
-  size_type find_last_of(const StringPiece& s, size_type pos = npos) const;
+  size_type find_last_of(const BasicStringPiece& s, size_type pos = npos) const;
   size_type find_last_of(char c, size_type pos = npos) const {
     return rfind(c, pos);
   }
-  size_type find_last_not_of(const StringPiece& s, size_type pos = npos) const;
+  size_type find_last_not_of(const BasicStringPiece& s,
+                             size_type pos = npos) const;
   size_type find_last_not_of(char c, size_type pos = npos) const;
 
-  StringPiece substr(size_type pos, size_type n = npos) const;
-
-  static int wordmemcmp(const char* p, const char* p2, size_type N) {
-    return memcmp(p, p2, N);
-  }
-
- private:
-  const char*   ptr_;
-  size_type     length_;
+  BasicStringPiece substr(size_type pos, size_type n = npos) const;
 };
 
-class BASE_EXPORT StringPiece16 {
- public:
-  // standard STL container boilerplate
-  typedef size_t size_type;
-  typedef char16 value_type;
-  typedef const char16* pointer;
-  typedef const char16& reference;
-  typedef const char16& const_reference;
-  typedef ptrdiff_t difference_type;
-  typedef const char16* const_iterator;
-  typedef const char16* iterator;
-  typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
-  typedef std::reverse_iterator<iterator> reverse_iterator;
+// MSVC doesn't like complex extern templates and DLLs.
+#if !defined(COMPILER_MSVC)
+extern template class BasicStringPiece<std::string>;

[Nico, 2011/12/19 21:58:26]

hans@ points out that declaring specialized templates (like
"BasicStringPiece<std::string>", which is specialized above) is a no-op, since
the specialization causes the template to be instantiated already.

[erikwright (departed), 2011/12/20 15:26:41]

Hmm. OK. The other concern would be the method definitions being duplicated in
many object files and not reconciled. But my intuition is that:

1) at worst only the methods used in a specific compilation unit would appear in
the object file, and most users only construct an instance before passing it
onto someone else.
2) even when methods are used, most of the methods amount to one or two
operations on a pointer that are probably cheaper than a function call anyway
and likely to be inlined.

So, thakis@ and hans@, would you say that it is harmless to simply remove the
externs here?

+extern template class BASE_EXPORT BasicStringPiece<string16>;
+#endif
 
- public:
-  // We provide non-explicit singleton constructors so users can pass
-  // in a "const char16*" or a "string16" wherever a "StringPiece16" is
-  // expected.
-  StringPiece16() : ptr_(NULL), length_(0) { }
-  StringPiece16(const char16* str)
-      : ptr_(str),
-        length_((str == NULL) ? 0 : string16::traits_type::length(str)) { }
-  StringPiece16(const string16& str)
-      : ptr_(str.data()), length_(str.size()) { }
-  StringPiece16(const char16* offset, size_type len)
-      : ptr_(offset), length_(len) { }
-
-  // data() may return a pointer to a buffer with embedded NULs, and the
-  // returned buffer may or may not be null terminated.  Therefore it is
-  // typically a mistake to pass data() to a routine that expects a NUL
-  // terminated string.
-  const char16* data() const { return ptr_; }
-  size_type size() const { return length_; }
-  size_type length() const { return length_; }
-  bool empty() const { return length_ == 0; }
-
-  void clear() {
-    ptr_ = NULL;
-    length_ = 0;
-  }
-  void set(const char16* data, size_type len) {
-    ptr_ = data;
-    length_ = len;
-  }
-  void set(const char16* str) {
-    ptr_ = str;
-    length_ = str ? string16::traits_type::length(str) : 0;
-  }
-
-  char16 operator[](size_type i) const { return ptr_[i]; }
-
-  string16 as_string16() const {
-    // StringPiece claims that this is bad when data() is NULL, but unittesting
-    // seems to say otherwise.
-    return string16(data(), size());
-  }
-
-  iterator begin() const { return ptr_; }
-  iterator end() const { return ptr_ + length_; }
-  const_reverse_iterator rbegin() const {
-    return const_reverse_iterator(ptr_ + length_);
-  }
-  const_reverse_iterator rend() const {
-    return const_reverse_iterator(ptr_);
-  }
-
-  size_type max_size() const { return length_; }
-  size_type capacity() const { return length_; }
-
-  static int wordmemcmp(const char16* p, const char16* p2, size_type N) {
-    return string16::traits_type::compare(p, p2, N);
-  }
-
- private:
-  const char16*   ptr_;
-  size_type       length_;
-};
+typedef BasicStringPiece<std::string> StringPiece;
+typedef BasicStringPiece<string16> StringPiece16;
 
 BASE_EXPORT bool operator==(const StringPiece& x, const StringPiece& y);
 
 inline bool operator!=(const StringPiece& x, const StringPiece& y) {
   return !(x == y);
 }
 
 inline bool operator<(const StringPiece& x, const StringPiece& y) {
   const int r = StringPiece::wordmemcmp(
       x.data(), y.data(), (x.size() < y.size() ? x.size() : y.size()));
@@ skipping 79 matching lines @@
 }
 inline size_t hash_value(const base::StringPiece16& sp16) {
   HASH_STRING_PIECE(base::StringPiece16, sp16);
 }
 
 #endif  // COMPILER
 
 }  // namespace BASE_HASH_NAMESPACE
 
 #endif  // BASE_STRING_PIECE_H_