gecko-dev/xpcom/string/public/nsAReadableString.h

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/*
 * The contents of this file are subject to the Netscape Public
 * License Version 1.1 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
 * the License at http://www.mozilla.org/NPL/
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 *
 * The Original Code is mozilla.org code.
 *
 * The Initial Developer of the Original Code is Netscape
 * Communications Corporation.  Portions created by Netscape are
 * Copyright (C) 1998 Netscape Communications Corporation. All
 * Rights Reserved.
 *
 * Contributor(s):
 *   Scott Collins <scc@netscape.com>
 */

#ifndef _nsAReadableString_h__
#define _nsAReadableString_h__

  // WORK IN PROGRESS

#include "nscore.h"
  // for |PRUnichar|

#include <string>
  // for |char_traits|

#include <iterator>
  // for |bidirectional_iterator_tag|


/*
  This file defines the abstract interfaces |nsAReadableString| and
  |nsAReadableCString| (the 'A' is for 'abstract', as opposed to the 'I' in
  [XP]COM interface names).

  These types are intended to be as source compatible as possible with the original
  definitions of |const nsString&| and |const nsCString&|, respectively.  In otherwords,
  these interfaces provide only non-mutating access to the underlying strings.  We
  split the these interfaces out from the mutating parts (see
  "nsAWritableString.h") because tests showed that we could exploit specialized
  implementations in some areas; we need an abstract interface to bring the whole
  family of strings together.

  |nsAReadableString| is a string of |PRUnichar|s.  |nsAReadableCString| (note the
  'C') is a string of |char|s.
*/


template <class CharT> class basic_nsAWritableString;
  // ...because we sometimes use them as `out' params

template <class CharT> class basic_nsLiteralString;
  // ...because we sometimes use them as in params to force the conversion of |CharT*|s






  //
  // nsAReadable[C]String
  //

template <class CharT>
class basic_nsAReadableString
    /*
      ...
    */
  {
    protected:

      struct ConstFragment
        {
          const CharT*  mStart;
          const CharT*  mEnd;
          PRUint32      mFragmentIdentifier;

          ConstFragment()
              : mStart(0), mEnd(0), mFragmentIdentifier(0)
            {
              // nothing else to do here
            }
        };

    public:
      enum FragmentRequest { kPrevFragment, kFirstFragment, kLastFragment, kNextFragment, kFragmentAt };

        // Damn!  Had to make |GetConstFragment| and |Implementation| public because the compilers suck.  Should be protected.
      virtual const char* Implementation() const;
      virtual const CharT* GetConstFragment( ConstFragment&, FragmentRequest, PRUint32 = 0 ) const = 0;

      friend class ConstIterator;
      class ConstIterator
            : public std::bidirectional_iterator_tag
        {
          public:
            typedef ptrdiff_t                   difference_type;
            typedef CharT                       value_type;
            typedef const CharT*                pointer;
            typedef const CharT&                reference;
            typedef bidirectional_iterator_tag  iterator_category;

          private:
            friend class basic_nsAReadableString<CharT>;

            ConstFragment mFragment;
            const CharT*  mPosition;
            const basic_nsAReadableString<CharT>* mOwningString;

            void
            normalize_forward()
              {
                if ( mPosition == mFragment.mEnd )
                  if ( mOwningString->GetConstFragment(mFragment, kNextFragment) )
                    mPosition = mFragment.mStart;
              }

            void
            normalize_backward()
              {
                if ( mPosition == mFragment.mStart )
                  if ( mOwningString->GetConstFragment(mFragment, kPrevFragment) )
                    mPosition = mFragment.mEnd;
              }

            ConstIterator( const ConstFragment& aFragment,
                           const CharT* aStartingPosition,
                           const basic_nsAReadableString<CharT>& aOwningString )
                : mFragment(aFragment),
                  mPosition(aStartingPosition),
                  mOwningString(&aOwningString)
              {
                // nothing else to do here
              }

          public:
            // ConstIterator( const ConstIterator& ); ...use default copy-constructor
            // ConstIterator& operator=( const ConstIterator& ); ...use default copy-assignment operator

            
            CharT
            operator*()
              {
                return *mPosition;
              }

            ConstIterator&
            operator++()
              {
                ++mPosition;
                normalize_forward();
                return *this;
              }

            ConstIterator
            operator++( int )
              {
                ConstIterator result(*this);
                ++mPosition;
                normalize_forward();
                return result;
              }

            ConstIterator&
            operator--()
              {
                normalize_backward();
                --mPosition;
                return *this;
              }

            ConstIterator
            operator--( int )
              {
                ConstIterator result(*this);
                normalize_backward();
                --mPosition;
                return result;
              }


              // Damn again!  Problems with templates made me implement comparisons as members.

            PRBool
            operator==( const ConstIterator& rhs )
              {
                return mPosition == rhs.mPosition;
              }

            PRBool
            operator!=( const ConstIterator& rhs )
              {
                return mPosition != rhs.mPosition;
              }
        };


    public:

      ConstIterator
      Begin( PRUint32 aOffset = 0 ) const
        {
          ConstFragment fragment;
          const CharT* startPos = GetConstFragment(fragment, kFragmentAt, aOffset);
          return ConstIterator(fragment, startPos, *this);
        }

      ConstIterator
      End( PRUint32 aOffset = 0 ) const
        {
          ConstFragment fragment;
          const CharT* startPos = GetConstFragment(fragment, kFragmentAt, max(0U, Length()-aOffset));
          return ConstIterator(fragment, startPos, *this);
        }

    public:
      virtual ~basic_nsAReadableString<CharT>() { }
        // ...yes, I expect to be sub-classed.

      virtual PRUint32 Length() const = 0;

      PRBool
      IsEmpty() const
        {
          return Length() == 0;
        }



        /*
          RickG says the following three routines, |IsUnicode()|, |GetBuffer()|, and |GetUnicode()|
          shouldn't be implemented because they're wrong access.  I agree.  Callers who really need
          this access should use the iterators instead.  We'll use these to ease the transition to
          |nsAReadable...|, and then remove them as soon as possible.
        */

      PRBool IsUnicode() const { return PR_FALSE; }
        // ...but note specialization for |PRUnichar|, below

      const char* GetBuffer() const { return 0; }
      const PRUnichar* GetUnicode() const { return 0; }
        // ...but note specializations for |char| and |PRUnichar|, below



      CharT CharAt( PRUint32 ) const;
      CharT operator[]( PRUint32 ) const;
      CharT First() const;
      CharT Last() const;

      PRUint32 CountChar( CharT ) const;

      PRUint32 Left( basic_nsAWritableString<CharT>&, PRUint32 ) const;
      PRUint32 Mid( basic_nsAWritableString<CharT>&, PRUint32, PRUint32 ) const;
      PRUint32 Right( basic_nsAWritableString<CharT>&, PRUint32 ) const;

      // Find( ... ) const;
      // FindChar( ... ) const;
      // FindCharInSet( ... ) const;
      // RFind( ... ) const;
      // RFindChar( ... ) const;
      // RFindCharInSet( ... ) const;

      int Compare( const basic_nsAReadableString<CharT>& rhs ) const;
      int Compare( const basic_nsLiteralString<CharT>& rhs ) const;


        // |Equals()| is a synonym for |Compare()|

      PRBool
      Equals( const basic_nsAReadableString<CharT>& rhs ) const
        {
          return Compare(rhs) == 0;
        }

      PRBool
      Equals( const basic_nsLiteralString<CharT>& rhs ) const
        {
          return Compare(rhs) == 0;
        }


        /*
          Shouldn't be implemented because they're i18n sensitive.
          Let's leave them in |nsString| for now.
        */

      // ToLowerCase
      // ToUpperCase
      // EqualsIgnoreCase
      // IsASCII
      // IsSpace
      // IsAlpha
      // IsDigit
      // ToFloat
      // ToInteger

      // char* ToNewCString() const;
      // char* ToNewUTF8String() const;
      // PRUnichar* ToNewUnicode() const;
      // char* ToCString( char*, PRUint32, PRUint32 ) const;


        /*
          Shouldn't be implemented because it's wrong duplication.
          Let's leave it in |nsString| for now.
        */

      // nsString* ToNewString() const;
        // NO!  The right way to say this is |new nsString( fromAReadableString )|


        /*
          Shouldn't be implemented because they're not generally applicable.
          Let's leave them in |nsString| for now.
        */

      // IsOrdered
      // BinarySearch



        // Comparison operators are all synonyms for |Compare()|

      PRBool operator!=( const basic_nsAReadableString<CharT>& rhs ) const { return Compare(rhs)!=0; }
      PRBool operator< ( const basic_nsAReadableString<CharT>& rhs ) const { return Compare(rhs)< 0; }
      PRBool operator<=( const basic_nsAReadableString<CharT>& rhs ) const { return Compare(rhs)<=0; }
      PRBool operator==( const basic_nsAReadableString<CharT>& rhs ) const { return Compare(rhs)==0; }
      PRBool operator>=( const basic_nsAReadableString<CharT>& rhs ) const { return Compare(rhs)>=0; }
      PRBool operator> ( const basic_nsAReadableString<CharT>& rhs ) const { return Compare(rhs)> 0; }
  };

#define NS_DEF_1_STRING_COMPARISON_OPERATOR(comp, T1, T2) \
  template <class CharT>                        \
  inline                                        \
  PRBool                                        \
  operator comp( T1 lhs, T2 rhs )               \
    {                                           \
      return PRBool(Compare(lhs, rhs) comp 0);  \
    }

#define NS_DEF_STRING_COMPARISON_OPERATORS(T1, T2) \
  NS_DEF_1_STRING_COMPARISON_OPERATOR(!=, T1, T2) \
  NS_DEF_1_STRING_COMPARISON_OPERATOR(< , T1, T2) \
  NS_DEF_1_STRING_COMPARISON_OPERATOR(<=, T1, T2) \
  NS_DEF_1_STRING_COMPARISON_OPERATOR(==, T1, T2) \
  NS_DEF_1_STRING_COMPARISON_OPERATOR(>=, T1, T2) \
  NS_DEF_1_STRING_COMPARISON_OPERATOR(> , T1, T2)

#define NS_DEF_STRING_COMPARISONS(T) \
  NS_DEF_STRING_COMPARISON_OPERATORS(const T&, const CharT*) \
  NS_DEF_STRING_COMPARISON_OPERATORS(const CharT*, const T&)


NS_DEF_STRING_COMPARISONS(basic_nsAReadableString<CharT>)



NS_SPECIALIZE_TEMPLATE
inline
PRBool
basic_nsAReadableString<PRUnichar>::IsUnicode() const
  {
    return PR_TRUE;
  }

NS_SPECIALIZE_TEMPLATE
inline
const char*
basic_nsAReadableString<char>::GetBuffer() const
    // DEPRECATED: use the iterators instead
  {
    ConstFragment fragment;
    GetConstFragment(fragment, kFirstFragment);
    return fragment.mStart;
  }

NS_SPECIALIZE_TEMPLATE
inline
const PRUnichar*
basic_nsAReadableString<PRUnichar>::GetUnicode() const
    // DEPRECATED: use the iterators instead
  {
    ConstFragment fragment;
    GetConstFragment(fragment, kFirstFragment);
    return fragment.mStart;
  }

template <class CharT>
const char*
basic_nsAReadableString<CharT>::Implementation() const
  {
    return 0;
  }



  /*
    Note: the following four functions, |CharAt|, |operator[]|, |First|, and |Last|, are implemented
    in the simplest reasonable scheme; by calling |GetConstFragment| and resolving the pointer it
    returns.  The alternative is to force at least one of these methods to be |virtual|.  The ideal
    candidate for that change would be |CharAt|.

    This is something to measure in the context of how string classes are actually used.  In practice,
    do people extract a character at a time in performance critical places?  If so, can they use
    iterators instead?  If they must extract single characters, _and_ they can't use iterators, _and_
    it happens enough to notice, then we'll take the hit and make |CharAt| virtual.
  */

template <class CharT>
inline
CharT
basic_nsAReadableString<CharT>::CharAt( PRUint32 aIndex ) const
  {
      // ??? Is |CharAt()| supposed to be the 'safe' version?
    ConstFragment fragment;
    return *GetConstFragment(fragment, kFragmentAt, aIndex);
  }

template <class CharT>
inline
CharT
basic_nsAReadableString<CharT>::operator[]( PRUint32 aIndex ) const
  {
    return CharAt(aIndex);
  }

template <class CharT>
inline
CharT
basic_nsAReadableString<CharT>::First() const
  {
    return CharAt(0);
  }

template <class CharT>
inline
CharT
basic_nsAReadableString<CharT>::Last() const
  {
    return CharAt(Length()-1);
  }

template <class CharT>
PRUint32
basic_nsAReadableString<CharT>::CountChar( CharT c ) const
  {
    return PRUint32(count(Begin(), End(), c));
  }


  /*
    Note: |Left()|, |Mid()|, and |Right()| could be modified to notice when they degenerate into copying the
    entire string, and call |Assign()| instead.  This would be a win when the underlying implementation of
    both strings could do buffer sharing.  This is _definitely_ something that should be measured before
    being implemented.
  */

template <class CharT>
PRUint32
basic_nsAReadableString<CharT>::Left( basic_nsAWritableString<CharT>& aResult, PRUint32 aLengthToCopy ) const
  {
    aResult = Substring(*this, 0, aLengthToCopy);
    return aResult.Length();
  }

template <class CharT>
PRUint32
basic_nsAReadableString<CharT>::Mid( basic_nsAWritableString<CharT>& aResult, PRUint32 aStartPos, PRUint32 aLengthToCopy ) const
  {
    aResult = Substring(*this, aStartPos, aLengthToCopy);
    return aResult.Length();
  }

template <class CharT>
PRUint32
basic_nsAReadableString<CharT>::Right( basic_nsAWritableString<CharT>& aResult, PRUint32 aLengthToCopy ) const
  {
    PRUint32 myLength = Length();
    aLengthToCopy = min(myLength, aLengthToCopy);
    aResult = Substring(*this, myLength-aLengthToCopy, aLengthToCopy);
    return aResult.Length();
  }



template <class CharT>
inline
int
basic_nsAReadableString<CharT>::Compare( const basic_nsAReadableString<CharT>& rhs ) const
  {
    return ::Compare(*this, rhs);
  }

template <class CharT>
inline
int
basic_nsAReadableString<CharT>::Compare( const basic_nsLiteralString<CharT>& rhs ) const
  {
    return ::Compare(*this, rhs);
  }






  //
  // nsLiteral[C]String
  //

template <class CharT>
class basic_nsLiteralString
      : public basic_nsAReadableString<CharT>
    /*
      ...this class wraps a constant literal string and lets it act like an |nsAReadable...|.
      
      Use it like this:

        SomeFunctionTakingACString( nsLiteralCString("Hello, World!") );

      With some tweaking, I think I can make this work as well...

        SomeStringFunc( nsLiteralString( L"Hello, World!" ) );

      This class just holds a pointer.  If you don't supply the length, it must calculate it.
      No copying or allocations are performed.

      |const basic_nsLiteralString<CharT>&| appears frequently in interfaces because it
      allows the automatic conversion of a |CharT*|.
    */
  {
    typedef typename basic_nsAReadableString<CharT>::FragmentRequest  FragmentRequest;
    typedef typename basic_nsAWritableString<CharT>::ConstFragment    ConstFragment;

    protected:
      virtual const CharT* GetConstFragment( ConstFragment&, FragmentRequest, PRUint32 ) const;

    public:
    
        // Note: _not_ explicit
      basic_nsLiteralString( const CharT* aLiteral )
          : mStart(aLiteral),
            mEnd(mStart + char_traits<CharT>::length(mStart))
        {
          // nothing else to do here
        }

      basic_nsLiteralString( const CharT* aLiteral, PRUint32 aLength )
          : mStart(aLiteral)
            mEnd(mStart + aLength)
        {
          // nothing else to do here
        }

      virtual PRUint32 Length() const;

    private:
      const CharT* mStart;
      const CharT* mEnd;
  };

NS_DEF_STRING_COMPARISONS(basic_nsLiteralString<CharT>)

template <class CharT>
const CharT*
basic_nsLiteralString<CharT>::GetConstFragment( ConstFragment& aFragment, FragmentRequest aRequest, PRUint32 aOffset ) const
  {
    switch ( aRequest )
      {
        case kFirstFragment:
        case kLastFragment:
        case kFragmentAt:
          aFragment.mStart = mStart;
          aFragment.mEnd = mEnd;
          return mStart + aOffset;
        
        case kPrevFragment:
        case kNextFragment:
        default:
          return 0;
      }
  }

template <class CharT>
PRUint32
basic_nsLiteralString<CharT>::Length() const
  {
    return PRUint32(mEnd - mStart);
  }






  //
  // nsPromiseConcatenation
  //

template <class CharT>
class nsPromiseConcatenation
      : public basic_nsAReadableString<CharT>
    /*
      NOT FOR USE BY HUMANS

      Instances of this class only exist as anonymous temporary results from |operator+()|.
      This is the machinery that makes string concatenation efficient.  No allocations or
      character copies are required unless and until a final assignment is made.  It works
      its magic by overriding and forwarding calls to |GetConstFragment()|.

      Note: |nsPromiseConcatenation| imposes some limits on string concatenation with |operator+()|.
        - no more than 33 strings, e.g., |s1 + s2 + s3 + ... s32 + s33|
        - left to right evaluation is required ... do not use parentheses to override this

      In practice, neither of these is onerous.  Parentheses do not change the semantics of the
      concatenation, only the order in which the result is assembled ... so there's no reason
      for a user to need to control it.  Too many strings summed together can easily be worked
      around with an intermediate assignment.  I wouldn't have the parentheses limitation if I
      assigned the identifier mask starting at the top, the first time anybody called
      |GetConstFragment()|.
    */
  {
    typedef typename basic_nsAReadableString<CharT>::FragmentRequest  FragmentRequest;
    typedef typename basic_nsAWritableString<CharT>::ConstFragment    ConstFragment;

    protected:
      virtual const CharT* GetConstFragment( ConstFragment&, FragmentRequest, PRUint32 ) const;

      static const int kLeftString = 0;
      static const int kRightString = 1;

      int
      GetCurrentStringFromFragment( const ConstFragment& aFragment ) const
        {
          return (aFragment.mFragmentIdentifier & mFragmentIdentifierMask) ? kRightString : kLeftString;
        }

      int
      SetLeftStringInFragment( ConstFragment& aFragment ) const
        {
          aFragment.mFragmentIdentifier &= ~mFragmentIdentifierMask;
          return kLeftString;
        }

      int
      SetRightStringInFragment( ConstFragment& aFragment ) const
        {
          aFragment.mFragmentIdentifier |= mFragmentIdentifierMask;
          return kRightString;
        }

    public:
      nsPromiseConcatenation( const basic_nsAReadableString<CharT>& aLeftString, const basic_nsAReadableString<CharT>& aRightString, PRUint32 aMask = 1 )
          : mFragmentIdentifierMask(aMask)
        {
          mStrings[kLeftString] = &aLeftString;
          mStrings[kRightString] = &aRightString;
        }

      virtual PRUint32 Length() const;

      nsPromiseConcatenation<CharT> operator+( const basic_nsAReadableString<CharT>& rhs ) const;

    private:
      void operator+( const nsPromiseConcatenation<CharT>& ); // NOT TO BE IMPLEMENTED
        // making this |private| stops you from over parenthesizing concatenation expressions, e.g., |(A+B) + (C+D)|
        //  which would break the algorithm for distributing bits in the fragment identifier

    private:
      const basic_nsAReadableString<CharT>* mStrings[2];
      PRUint32 mFragmentIdentifierMask;
  };

NS_DEF_STRING_COMPARISONS(nsPromiseConcatenation<CharT>)

template <class CharT>
PRUint32
nsPromiseConcatenation<CharT>::Length() const
  {
    return mStrings[kLeftString]->Length() + mStrings[kRightString]->Length();
  }

template <class CharT>
const CharT*
nsPromiseConcatenation<CharT>::GetConstFragment( ConstFragment& aFragment, FragmentRequest aRequest, PRUint32 aPosition ) const
  {
    const int kLeftString   = 0;
    const int kRightString  = 1;

    int whichString;

      // based on the request, pick which string we will forward the |GetConstFragment()| call into

    switch ( aRequest )
      {
        case kPrevFragment:
        case kNextFragment:
          whichString = GetCurrentStringFromFragment(aFragment);
          break;

        case kFirstFragment:
          whichString = SetLeftStringInFragment(aFragment);
          break;

        case kLastFragment:
          whichString = SetRightStringInFragment(aFragment);
          break;

        case kFragmentAt:
          PRUint32 leftLength = mStrings[kLeftString]->Length();
          if ( aPosition < leftLength )
            whichString = SetLeftStringInFragment(aFragment);
          else
            {
              whichString = SetRightStringInFragment(aFragment);
              aPosition -= leftLength;
            }
          break;
            
      }

    const CharT* result;
    bool done;
    do
      {
        done = true;
        result = mStrings[whichString]->GetConstFragment(aFragment, aRequest, aPosition);

        if ( !result )
          {
            done = false;
            if ( aRequest == kNextFragment && whichString == kLeftString )
              {
                aRequest = kFirstFragment;
                whichString = SetRightStringInFragment(aFragment);
              }
            else if ( aRequest == kPrevFragment && whichString == kRightString )
              {
                aRequest = kLastFragment;
                whichString = SetLeftStringInFragment(aFragment);
              }
            else
              done = true;
          }
      }
    while ( !done );
    return result;
  }

template <class CharT>
nsPromiseConcatenation<CharT>
nsPromiseConcatenation<CharT>::operator+( const basic_nsAReadableString<CharT>& rhs ) const
  {
    return nsPromiseConcatenation<CharT>(*this, rhs, mFragmentIdentifierMask<<1);
  }






  //
  // nsPromiseSubstring
  //

template <class CharT>
class nsPromiseSubstring
      : public basic_nsAReadableString<CharT>
    /*
      NOT FOR USE BY HUMANS (mostly)

      ...not unlike |nsPromiseConcatenation|.  Instances of this class exist only as anonymous
      temporary results from |Substring()|.  Like |nsPromiseConcatenation|, this class only
      holds a pointer, no string data of its own.  It does its magic by overriding and forwarding
      calls to |GetConstFragment()|.
    */
  {
    typedef typename basic_nsAReadableString<CharT>::FragmentRequest  FragmentRequest;
    typedef typename basic_nsAWritableString<CharT>::ConstFragment    ConstFragment;

    protected:
      virtual const CharT* GetConstFragment( ConstFragment&, FragmentRequest, PRUint32 ) const;

    public:
      nsPromiseSubstring( const basic_nsAReadableString<CharT>& aString, PRUint32 aStartPos, PRUint32 aLength )
          : mString(aString),
            mStartPos( min(aStartPos, aString.Length()) ),
            mLength( min(aLength, aString.Length()-mStartPos) )
        {
          // nothing else to do here
        }

      virtual PRUint32 Length() const;

    private:
      const basic_nsAReadableString<CharT>& mString;
      PRUint32 mStartPos;
      PRUint32 mLength;
  };

NS_DEF_STRING_COMPARISONS(nsPromiseSubstring<CharT>)

template <class CharT>
PRUint32
nsPromiseSubstring<CharT>::Length() const
  {
    return mLength;
  }

template <class CharT>
const CharT*
nsPromiseSubstring<CharT>::GetConstFragment( ConstFragment& aFragment, FragmentRequest aRequest, PRUint32 aPosition ) const
  {
      // Offset any request for a specific position (First, Last, At) by our
      //  substrings startpos within the owning string

    if ( aRequest == kFirstFragment )
      {
        aPosition = mStartPos;
        aRequest = kFragmentAt;
      }
    else if ( aRequest == kLastFragment )
      {
        aPosition = mStartPos + mLength;
        aRequest = kFragmentAt;
      }
    else if ( aRequest == kFragmentAt )
      aPosition += mStartPos;

    return mString.GetConstFragment(aFragment, aRequest, aPosition);
  }






  //
  // Global functions
  //

template <class CharT>
nsPromiseSubstring<CharT>
Substring( const basic_nsAReadableString<CharT>& aString, PRUint32 aStartPos, PRUint32 aSubstringLength )
  {
    return nsPromiseSubstring<CharT>(aString, aStartPos, aSubstringLength);
  }


template <class CharT>
int
Compare( const basic_nsAReadableString<CharT>& lhs, const basic_nsAReadableString<CharT>& rhs )
  {
      /*
        If this turns out to be too slow (after measurement), there are two important modifications
          1) chunky iterators
          2) and then possibly use |char_traits<T>::compare|
      */

    PRUint32 lLength = lhs.Length();
    PRUint32 rLength = rhs.Length();
    PRUint32 lengthToCompare = min(lLength, rLength);

    typedef typename basic_nsAReadableString<CharT>::ConstIterator ConstIterator;
    ConstIterator lPos = lhs.Begin();
    ConstIterator lEnd = lhs.Begin(lengthToCompare);
    ConstIterator rPos = rhs.Begin();

    while ( lPos != lEnd )
      {
        if ( *lPos < *rPos )
          return -1;
        if ( *rPos < *lPos )
          return 1;

        ++lPos;
        ++rPos;
      }

    if ( lLength < rLength )
      return -1;
    else if ( rLength < lLength )
      return 1;
    else
      return 0;
  }

template <class CharT>
inline
int
Compare( const basic_nsAReadableString<CharT>& lhs, const CharT* rhs )
  {
    return Compare(lhs, basic_nsLiteralString<CharT>(rhs));
  }

template <class CharT>
inline
int
Compare( const CharT* lhs, const basic_nsAReadableString<CharT>& rhs )
  {
    return Compare(basic_nsLiteralString<CharT>(lhs), rhs);
  }



  /*
    How shall we provide |operator+()|?

    What would it return?  It has to return a stack based object, because the client will
    not be given an opportunity to handle memory management in an expression like

      myWritableString = stringA + stringB + stringC;

    ...so the `obvious' answer of returning a new |nsSharedString| is no good.  We could
    return an |nsString|, if that name were in scope here, though there's no telling what the client
    will really want to do with the result.  What might be better, though,
    is to return a `promise' to concatenate some strings...

    By making |nsPromiseConcatenation| inherit from readable strings, we automatically handle
    assignment and other interesting uses within writable strings, plus we drastically reduce
    the number of cases we have to write |operator+()| for.  The cost is extra temporary concat strings
    in the evaluation of strings of '+'s, e.g., |A + B + C + D|, and that we have to do some work
    to implement the virtual functions of readables.
  */

template <class CharT>
nsPromiseConcatenation<CharT>
operator+( const basic_nsAReadableString<CharT>& lhs, const basic_nsAReadableString<CharT>& rhs )
  {
    return nsPromiseConcatenation<CharT>(lhs, rhs);
  }

template <class CharT>
nsPromiseConcatenation<CharT>
operator+( const basic_nsAReadableString<CharT>& lhs, const basic_nsLiteralString<CharT>& rhs )
  {
    return nsPromiseConcatenation<CharT>(lhs, rhs);
  }

template <class CharT>
nsPromiseConcatenation<CharT>
operator+( const basic_nsLiteralString<CharT>& lhs, const basic_nsAReadableString<CharT>& rhs )
  {
    return nsPromiseConcatenation<CharT>(lhs, rhs);
  }

template <class CharT>
nsPromiseConcatenation<CharT>
operator+( const basic_nsLiteralString<CharT>& lhs, const basic_nsLiteralString<CharT>& rhs )
  {
    return nsPromiseConcatenation<CharT>(lhs, rhs);
  }




template <class CharT, class TraitsT>
basic_ostream<CharT, class TraitsT>&
operator<<( basic_ostream<CharT, TraitsT>& os, const basic_nsAReadableString<CharT>& s )
  {
    std::copy(s.Begin(), s.End(), ostream_iterator<CharT, CharT, TraitsT>(os));
    return os;
  }

typedef basic_nsAReadableString<PRUnichar>  nsAReadableString;
typedef basic_nsAReadableString<char>       nsAReadableCString;

typedef basic_nsLiteralString<PRUnichar>    nsLiteralString;
typedef basic_nsLiteralString<char>         nsLiteralCString;

#endif // !defined(_nsAReadableString_h__)