StrBlob.h

/*
 * This file contains code from "C++ Primer, Fifth Edition", by Stanley B.
 * Lippman, Josee Lajoie, and Barbara E. Moo, and is covered under the
 * copyright and warranty notices given in that book:
 * 
 * "Copyright (c) 2013 by Objectwrite, Inc., Josee Lajoie, and Barbara E. Moo."
 * 
 * 
 * "The authors and publisher have taken care in the preparation of this book,
 * but make no expressed or implied warranty of any kind and assume no
 * responsibility for errors or omissions. No liability is assumed for
 * incidental or consequential damages in connection with or arising out of the
 * use of the information or programs contained herein."
 * 
 * Permission is granted for this code to be used for educational purposes in
 * association with the book, given proper citation if and when posted or
 * reproduced. Any commercial use of this code requires the explicit written
 * permission of the publisher, Addison-Wesley Professional, a division of
 * Pearson Education, Inc. Send your request for permission, stating clearly
 * what code you would like to use, and in what specific way, to the following
 * address: 
 * 
 * 	Pearson Education, Inc.
 * 	Rights and Permissions Department
 * 	One Lake Street
 * 	Upper Saddle River, NJ  07458
 * 	Fax: (201) 236-3290
*/

#ifndef STRBLOB_H
#define STRBLOB_H

#include <vector>
#include <string>
#include <initializer_list>
#include <memory>
#include <stdexcept>

// forward declaration needed for friend declaration in StrBlob
class StrBlobPtr;

class StrBlob
{
	friend class StrBlobPtr;
public:
    typedef std::vector<std::string>::size_type size_type;

	// constructors
    StrBlob() : data(std::make_shared<std::vector<std::string>>()) { }
    StrBlob(std::initializer_list<std::string> il);

	// size operations
    size_type size() const { return data->size(); }
    bool empty() const { return data->empty(); }

    // add and remove elements
    void push_back(const std::string &t) { data->push_back(t); }
    void pop_back();

    // element access
    std::string& front();
    std::string& back();

	// interface to StrBlobPtr
	StrBlobPtr begin();  // can't be defined until StrBlobPtr is
    StrBlobPtr end();
private:
    std::shared_ptr<std::vector<std::string>> data; 
    // throws msg if data[i] isn't valid
    void check(size_type i, const std::string &msg) const;
};

// constructor
inline
StrBlob::StrBlob(std::initializer_list<std::string> il): 
              data(std::make_shared<std::vector<std::string>>(il)) { }

// StrBlobPtr throws an exception on attempts to access a nonexistent element 
class StrBlobPtr
{
	friend bool eq(const StrBlobPtr&, const StrBlobPtr&);
public:
    StrBlobPtr(): curr(0) { }
    StrBlobPtr(StrBlob &a, size_t sz = 0) : wptr(a.data), curr(sz) { }

    //! newly overloaded why?
    StrBlobPtr(const StrBlob &a, const size_t sz = 0) : wptr(a.data), curr(sz) { }

    std::string& deref() const;
    StrBlobPtr& incr();       // prefix version
    StrBlobPtr& decr();       // prefix version
private:
    // check returns a shared_ptr to the vector if the check succeeds
    std::shared_ptr<std::vector<std::string>> 
        check(std::size_t, const std::string&) const;

    // store a weak_ptr, which means the underlying vector might be destroyed
    std::weak_ptr<std::vector<std::string>> wptr;  
    std::size_t curr;      // current position within the array
};

inline
std::string& StrBlobPtr::deref() const
{
    auto p = check(curr, "dereference past end"); 
    return (*p)[curr];  // (*p) is the vector to which this object points
}

inline
std::shared_ptr<std::vector<std::string>> 
StrBlobPtr::check(std::size_t i, const std::string &msg) const
{
    auto ret = wptr.lock();   // is the vector still around?
    if (!ret)
        throw std::runtime_error("unbound StrBlobPtr");

    if (i >= ret->size()) 
        throw std::out_of_range(msg);
    return ret; // otherwise, return a shared_ptr to the vector
}

// prefix: return a reference to the incremented object
inline
StrBlobPtr& StrBlobPtr::incr()
{
    // if curr already points past the end of the container, can't increment it
    check(curr, "increment past end of StrBlobPtr");
    ++curr;       // advance the current state
    return *this;
}

inline
StrBlobPtr& StrBlobPtr::decr()
{
    // if curr is zero, decrementing it will yield an invalid subscript
    --curr;       // move the current state back one element}
    check(-1, "decrement past begin of StrBlobPtr");
    return *this;
}

// begin and end members for StrBlob
inline
StrBlobPtr
StrBlob::begin() 
{
	return StrBlobPtr(*this);
}

inline
StrBlobPtr
StrBlob::end() 
{
	auto ret = StrBlobPtr(*this, data->size());
    return ret; 
}

// named equality operators for StrBlobPtr
inline
bool eq(const StrBlobPtr &lhs, const StrBlobPtr &rhs)
{
	auto l = lhs.wptr.lock(), r = rhs.wptr.lock();
	// if the underlying vector is the same 
	if (l == r) 
		// then they're equal if they're both null or 
		// if they point to the same element
		return (!r || lhs.curr == rhs.curr);
	else
		return false; // if they point to difference vectors, they're not equal
}

inline
bool neq(const StrBlobPtr &lhs, const StrBlobPtr &rhs)
{
	return !eq(lhs, rhs); 
}
#endif