зеркало из https://github.com/mozilla/gecko-dev.git
270 строки
10 KiB
C++
270 строки
10 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/*
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* The contents of this file are subject to the Mozilla Public
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* License Version 1.1 (the "License"); you may not use this file
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* except in compliance with the License. You may obtain a copy of
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* the License at http://www.mozilla.org/MPL/
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*
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* Software distributed under the License is distributed on an "AS
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* IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
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* implied. See the License for the specific language governing
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* rights and limitations under the License.
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*
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* The Original Code is Mozilla.
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*
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* The Initial Developer of the Original Code is Netscape
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* Communications. Portions created by Netscape Communications are
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* Copyright (C) 2001 by Netscape Communications. All
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* Rights Reserved.
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*
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* Contributor(s):
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* Scott Collins <scc@mozilla.org> (original author)
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*/
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/* nsPromiseConcatenation.h --- string concatenation machinery lives here, but don't include this file
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directly, always get it by including either "nsAString.h" or one of the compatibility headers */
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#ifndef nsPromiseConcatenation_h___
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#define nsPromiseConcatenation_h___
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/**
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NOT FOR USE BY HUMANS
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Instances of this class only exist as anonymous temporary results from |operator+()|.
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This is the machinery that makes string concatenation efficient. No allocations or
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character copies are required unless and until a final assignment is made. It works
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its magic by overriding and forwarding calls to |GetReadableFragment()|.
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Note: |nsPromiseConcatenation| imposes some limits on string concatenation with |operator+()|.
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- no more than 33 strings, e.g., |s1 + s2 + s3 + ... s32 + s33|
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- left to right evaluation is required ... do not use parentheses to override this
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In practice, neither of these is onerous. Parentheses do not change the semantics of the
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concatenation, only the order in which the result is assembled ... so there's no reason
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for a user to need to control it. Too many strings summed together can easily be worked
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around with an intermediate assignment. I wouldn't have the parentheses limitation if I
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assigned the identifier mask starting at the top, the first time anybody called
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|GetReadableFragment()|.
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*/
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class NS_COM nsPromiseConcatenation
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: public nsAPromiseString
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{
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public:
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typedef nsPromiseConcatenation self_type;
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typedef PRUnichar char_type;
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typedef nsAString string_type;
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typedef string_type::const_iterator const_iterator;
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protected:
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virtual const char_type* GetReadableFragment( nsReadableFragment<char_type>&, nsFragmentRequest, PRUint32 ) const;
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virtual char_type* GetWritableFragment( nsWritableFragment<char_type>&, nsFragmentRequest, PRUint32 ) { return 0; }
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enum { kLeftString, kRightString };
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int
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GetCurrentStringFromFragment( const nsReadableFragment<char_type>& aFragment ) const
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{
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return (NS_REINTERPRET_CAST(PRUint32, aFragment.mFragmentIdentifier) & mFragmentIdentifierMask) ? kRightString : kLeftString;
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}
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int
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SetLeftStringInFragment( nsReadableFragment<char_type>& aFragment ) const
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{
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aFragment.mFragmentIdentifier = NS_REINTERPRET_CAST(void*, NS_REINTERPRET_CAST(PRUint32, aFragment.mFragmentIdentifier) & ~mFragmentIdentifierMask);
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return kLeftString;
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}
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int
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SetRightStringInFragment( nsReadableFragment<char_type>& aFragment ) const
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{
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aFragment.mFragmentIdentifier = NS_REINTERPRET_CAST(void*, NS_REINTERPRET_CAST(PRUint32, aFragment.mFragmentIdentifier) | mFragmentIdentifierMask);
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return kRightString;
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}
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public:
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nsPromiseConcatenation( const string_type& aLeftString, const string_type& aRightString, PRUint32 aMask = 1 )
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: mFragmentIdentifierMask(aMask)
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{
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mStrings[kLeftString] = &aLeftString;
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mStrings[kRightString] = &aRightString;
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}
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nsPromiseConcatenation( const self_type& aLeftString, const string_type& aRightString )
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: mFragmentIdentifierMask(aLeftString.mFragmentIdentifierMask<<1)
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{
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mStrings[kLeftString] = &aLeftString;
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mStrings[kRightString] = &aRightString;
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}
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// nsPromiseConcatenation( const self_type& ); // auto-generated copy-constructor should be OK
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// ~nsPromiseConcatenation(); // auto-generated destructor OK
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private:
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// NOT TO BE IMPLEMENTED
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void operator=( const self_type& ); // we're immutable, you can't assign into a concatenation
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public:
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virtual PRUint32 Length() const;
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virtual PRBool Promises( const string_type& ) const;
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// virtual PRBool PromisesExactly( const string_type& ) const;
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// const self_type operator+( const string_type& rhs ) const;
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PRUint32 GetFragmentIdentifierMask() const { return mFragmentIdentifierMask; }
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private:
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void operator+( const self_type& ); // NOT TO BE IMPLEMENTED
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// making this |private| stops you from over parenthesizing concatenation expressions, e.g., |(A+B) + (C+D)|
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// which would break the algorithm for distributing bits in the fragment identifier
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private:
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const string_type* mStrings[2];
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PRUint32 mFragmentIdentifierMask;
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};
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class NS_COM nsPromiseCConcatenation
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: public nsAPromiseCString
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{
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public:
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typedef nsPromiseCConcatenation self_type;
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typedef char char_type;
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typedef nsACString string_type;
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typedef string_type::const_iterator const_iterator;
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protected:
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virtual const char_type* GetReadableFragment( nsReadableFragment<char_type>&, nsFragmentRequest, PRUint32 ) const;
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virtual char_type* GetWritableFragment( nsWritableFragment<char_type>&, nsFragmentRequest, PRUint32 ) { return 0; }
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enum { kLeftString, kRightString };
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int
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GetCurrentStringFromFragment( const nsReadableFragment<char_type>& aFragment ) const
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{
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return (NS_REINTERPRET_CAST(PRUint32, aFragment.mFragmentIdentifier) & mFragmentIdentifierMask) ? kRightString : kLeftString;
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}
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int
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SetLeftStringInFragment( nsReadableFragment<char_type>& aFragment ) const
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{
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aFragment.mFragmentIdentifier = NS_REINTERPRET_CAST(void*, NS_REINTERPRET_CAST(PRUint32, aFragment.mFragmentIdentifier) & ~mFragmentIdentifierMask);
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return kLeftString;
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}
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int
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SetRightStringInFragment( nsReadableFragment<char_type>& aFragment ) const
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{
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aFragment.mFragmentIdentifier = NS_REINTERPRET_CAST(void*, NS_REINTERPRET_CAST(PRUint32, aFragment.mFragmentIdentifier) | mFragmentIdentifierMask);
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return kRightString;
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}
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public:
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nsPromiseCConcatenation( const string_type& aLeftString, const string_type& aRightString, PRUint32 aMask = 1 )
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: mFragmentIdentifierMask(aMask)
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{
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mStrings[kLeftString] = &aLeftString;
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mStrings[kRightString] = &aRightString;
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}
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nsPromiseCConcatenation( const self_type& aLeftString, const string_type& aRightString )
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: mFragmentIdentifierMask(aLeftString.mFragmentIdentifierMask<<1)
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{
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mStrings[kLeftString] = &aLeftString;
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mStrings[kRightString] = &aRightString;
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}
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// nsPromiseCConcatenation( const self_type& ); // auto-generated copy-constructor should be OK
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// ~nsPromiseCConcatenation(); // auto-generated destructor OK
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private:
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// NOT TO BE IMPLEMENTED
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void operator=( const self_type& ); // we're immutable, you can't assign into a concatenation
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public:
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virtual PRUint32 Length() const;
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virtual PRBool Promises( const string_type& ) const;
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// virtual PRBool PromisesExactly( const string_type& ) const;
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// const self_type operator+( const string_type& rhs ) const;
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PRUint32 GetFragmentIdentifierMask() const { return mFragmentIdentifierMask; }
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private:
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void operator+( const self_type& ); // NOT TO BE IMPLEMENTED
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// making this |private| stops you from over parenthesizing concatenation expressions, e.g., |(A+B) + (C+D)|
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// which would break the algorithm for distributing bits in the fragment identifier
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private:
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const string_type* mStrings[2];
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PRUint32 mFragmentIdentifierMask;
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};
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/*
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How shall we provide |operator+()|?
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What would it return? It has to return a stack based object, because the client will
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not be given an opportunity to handle memory management in an expression like
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myWritableString = stringA + stringB + stringC;
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...so the `obvious' answer of returning a new |nsSharedString| is no good. We could
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return an |nsString|, if that name were in scope here, though there's no telling what the client
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will really want to do with the result. What might be better, though,
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is to return a `promise' to concatenate some strings...
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By making |nsPromiseConcatenation| inherit from readable strings, we automatically handle
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assignment and other interesting uses within writable strings, plus we drastically reduce
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the number of cases we have to write |operator+()| for. The cost is extra temporary concat strings
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in the evaluation of strings of '+'s, e.g., |A + B + C + D|, and that we have to do some work
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to implement the virtual functions of readables.
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*/
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inline
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const nsPromiseConcatenation
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operator+( const nsPromiseConcatenation& lhs, const nsAString& rhs )
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{
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return nsPromiseConcatenation(lhs, rhs, lhs.GetFragmentIdentifierMask()<<1);
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}
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inline
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const nsPromiseCConcatenation
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operator+( const nsPromiseCConcatenation& lhs, const nsACString& rhs )
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{
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return nsPromiseCConcatenation(lhs, rhs, lhs.GetFragmentIdentifierMask()<<1);
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}
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inline
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const nsPromiseConcatenation
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operator+( const nsAString& lhs, const nsAString& rhs )
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{
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return nsPromiseConcatenation(lhs, rhs);
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}
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inline
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const nsPromiseCConcatenation
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operator+( const nsACString& lhs, const nsACString& rhs )
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{
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return nsPromiseCConcatenation(lhs, rhs);
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}
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#if 0
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inline
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const nsPromiseConcatenation
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nsPromiseConcatenation::operator+( const string_type& rhs ) const
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{
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return nsPromiseConcatenation(*this, rhs, mFragmentIdentifierMask<<1);
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}
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inline
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const nsPromiseCConcatenation
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nsPromiseCConcatenation::operator+( const string_type& rhs ) const
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{
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return nsPromiseCConcatenation(*this, rhs, mFragmentIdentifierMask<<1);
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}
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#endif
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#endif /* !defined(nsPromiseConcatenation_h___) */
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