Reduce String CoW

By introducing an intermediate proxy class for the array subscript
operator for String and CharString we can control better when CowData
will actually CoW.

This should improve performance of String usage for most cases.

1 files changed, 33 insertions, 2 deletions

diff --git a/core/ustring.h b/core/ustring.h
index 8e4dbd8031..e7b13027ea 100644
--- a/core/ustring.h
+++ b/core/ustring.h
@@ -40,6 +40,36 @@
 	@author Juan Linietsky <reduzio@gmail.com>
 */
 
+template <class T>
+class CharProxy {
+	friend class CharString;
+	friend class String;
+
+	const int _index;
+	CowData<T> &_cowdata;
+
+	_FORCE_INLINE_ CharProxy(const int &p_index, CowData<T> &cowdata) :
+			_index(p_index),
+			_cowdata(cowdata) {}
+
+public:
+	_FORCE_INLINE_ operator T() const {
+		return _cowdata.get(_index);
+	}
+
+	_FORCE_INLINE_ const T *operator&() const {
+		return _cowdata.ptr() + _index;
+	}
+
+	_FORCE_INLINE_ void operator=(const T &other) const {
+		_cowdata.set(_index, other);
+	}
+
+	_FORCE_INLINE_ void operator=(const CharProxy<T> &other) const {
+		_cowdata.set(_index, other.operator T());
+	}
+};
+
 class CharString {
 
 	CowData<char> _cowdata;
@@ -53,8 +83,8 @@ public:
 	_FORCE_INLINE_ char get(int p_index) { return _cowdata.get(p_index); }
 	_FORCE_INLINE_ const char get(int p_index) const { return _cowdata.get(p_index); }
 	_FORCE_INLINE_ void set(int p_index, const char &p_elem) { _cowdata.set(p_index, p_elem); }
-	_FORCE_INLINE_ char &operator[](int p_index) { return _cowdata.get_m(p_index); }
 	_FORCE_INLINE_ const char &operator[](int p_index) const { return _cowdata.get(p_index); }
+	_FORCE_INLINE_ CharProxy<char> operator[](int p_index) { return CharProxy<char>(p_index, _cowdata); }
 
 	_FORCE_INLINE_ CharString() {}
 	_FORCE_INLINE_ CharString(const CharString &p_str) { _cowdata._ref(p_str._cowdata); }
@@ -107,8 +137,9 @@ public:
 	_FORCE_INLINE_ void set(int p_index, const CharType &p_elem) { _cowdata.set(p_index, p_elem); }
 	_FORCE_INLINE_ int size() const { return _cowdata.size(); }
 	Error resize(int p_size) { return _cowdata.resize(p_size); }
-	_FORCE_INLINE_ CharType &operator[](int p_index) { return _cowdata.get_m(p_index); }
+
 	_FORCE_INLINE_ const CharType &operator[](int p_index) const { return _cowdata.get(p_index); }
+	_FORCE_INLINE_ CharProxy<CharType> operator[](int p_index) { return CharProxy<CharType>(p_index, _cowdata); }
 
 	bool operator==(const String &p_str) const;
 	bool operator!=(const String &p_str) const;