Effective-CPP-Programs/StringProxy.cpp at master · ardbytes/Effective-CPP-Programs · GitHub

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#include <iostream.h>

// Proxy Classes ( Item 30 ). From More Effective C++

// Adds a proxy class to AutoRCObject.cpp to distinguish between

// read usage and write usage of operator[]

// References

// > Item 1: Distinguish between pointers and references

// > Item 2: Prefer C++-style class.

// > Item 5: Be wary of user-defined conversion functions.

// > Item 7: Gives a list of overloadable operators and otherwise

// > Item 17: Lazy evaluation.

// > Item 19: Understand the origin of temporary objects.

// > Item 29: Reference Counting

// See also:

// > Reference.cpp*

// > RCObject.cpp

// > AutoRCObject.cpp

class RCObject

{

protected:

RCObject();

RCObject( const RCObject& rhs );

RCObject& operator=( const RCObject& rhs );

virtual ~RCObject () = 0;

public:

void addReference ();

void removeReference();

void markUnshareable();

bool isShareable() const;

bool isShared ()const;

private:

int refCount;

bool shareable;

};

RCObject::RCObject()

:refCount(0), shareable(true) {}

RCObject::RCObject( const RCObject& )

:refCount(0), shareable(true){}

RCObject& RCObject::operator=( const RCObject& )

{ return *this; }

RCObject::~RCObject() {}

void RCObject::addReference() { refCount++; }

void RCObject::removeReference()

{ if ( --refCount == 0 ) delete this; }

void RCObject::markUnshareable ( )

{ shareable = false; }

bool RCObject::isShareable() const

{ return shareable; }

bool RCObject::isShared() const

{ return refCount > 1; }

template <class T>

class RCPtr

{

public:

RCPtr(T* realPtr=0 );

RCPtr(const RCPtr& rhs);

~RCPtr();

RCPtr& operator=(const RCPtr& rhs);

T* operator->() const;

T& operator*() const;

private:

T *pointee;

void init();

};

template<class T>

RCPtr<T>::RCPtr(T *realPtr):pointee(realPtr)

{

init();

}

template<class T>

RCPtr<T>::RCPtr(const RCPtr& rhs):pointee(rhs.pointee)

{

init();

}

template<class T>

void RCPtr<T>::init()

{

if ( pointee == 0 )

return;

if ( pointee->isShareable() == false )

{

pointee = new T(*pointee);

}

pointee->addReference();

}

template<class T>

RCPtr<T>& RCPtr<T>::operator=( const RCPtr& rhs )

{

if ( pointee == rhs.pointee )

return *this;

if ( pointee )

{

pointee->removeReference();

}

pointee = rhs.pointee;

init();

return *this;

}

template<class T>

RCPtr<T>::~RCPtr()

{

if ( pointee ) pointee->removeReference();

}

template<class T>

T* RCPtr<T>::operator->() const { return pointee; }

template<class T>

T& RCPtr<T>::operator*() const { return *pointee; }

class String

{

public:

class CharProxy

{

public:

CharProxy ( String& str, int index );

CharProxy& operator= (const CharProxy& rhs);

CharProxy& operator= (char c);

char * operator&();

const char * operator&() const;

operator char() const;

private:

String& theString;

int charIndex;

};

const CharProxy operator[] (int index)const; // See Item 1

CharProxy operator[] (int index); // See Item 1

friend class CharProxy;

String ( const char *initValue = "" );

void Print ( );

private:

struct StringValue: public RCObject

{

char *data;

StringValue( const char *initValue );

StringValue( const StringValue& rhs );

~StringValue ( );

};

RCPtr<StringValue> value;

};

String::StringValue::StringValue ( const char *initValue )

{

data = new char [strlen (initValue) + 1];

strcpy(data, initValue);

}

String::StringValue::StringValue( const StringValue& rhs )

{

data = new char[strlen(rhs.data) + 1];

strcpy(data, rhs.data);

}

String::StringValue::~StringValue()

{

delete [] data;

}

String::CharProxy::CharProxy(String& str, int index)

:theString(str), charIndex(index)

{

}

String::CharProxy& String::CharProxy::operator= (const CharProxy& rhs)

{

if ( theString.value->isShared())

{

theString.value = new StringValue(theString.value->data);

}

theString.value->data[charIndex] = rhs.theString.value->data[rhs.charIndex];

return *this;

}

String::CharProxy& String::CharProxy::operator= (char c)

{

if ( theString.value->isShared() )

{

theString.value = new StringValue(theString.value->data);

}

theString.value->data[charIndex] = c;

return *this;

}

char * String::CharProxy::operator&()

{

if ( theString.value->isShared() )

{

theString.value = new StringValue(theString.value->data);

}

theString.value->markUnshareable();

return &(theString.value->data[charIndex]);

}

const char * String::CharProxy::operator&() const

{

return &(theString.value->data[charIndex]);

}

String::CharProxy::operator char() const

{

return theString.value->data[charIndex];

}

const String::CharProxy String::operator[](int index)const

{

return CharProxy(const_cast<String&>(*this), index);

}

String::CharProxy String::operator[] (int index)

{

return CharProxy(*this, index);

}

String::String( const char *initValue )

:value ( new StringValue ( initValue ) )

{}

void String::Print()

{

cout << "Data: " << value->data << endl;

cout << "Shared: " << value->isShared() << endl;

cout << "Shareable: " << value->isShareable() << endl << endl;

}

int main ()

{

String s1("More Effective C++");

char *p = &s1[1];

s1.Print();

String s2 ("Hello");

s2 = s1;

*p = 'x';

s2.Print();

}

Effective-CPP-Programs/StringProxy.cpp at master · ardbytes/Effective-CPP-Programs · GitHub

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