/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* vim: set ts=8 sts=2 et sw=2 tw=80: */

/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef nsTPromiseFlatString_h

#define nsTPromiseFlatString_h

#include "nsTString.h"

/**

 * NOTE:

 *

 * Try to avoid flat strings.  |PromiseFlat[C]String| will help you as a last

 * resort, and this may be necessary when dealing with legacy or OS calls,

 * but in general, requiring a null-terminated array of characters kills many

 * of the performance wins the string classes offer.  Write your own code to

 * use |nsA[C]String&|s for parameters.  Write your string proccessing

 * algorithms to exploit iterators.  If you do this, you will benefit from

 * being able to chain operations without copying or allocating and your code

 * will be significantly more efficient.  Remember, a function that takes an

 * |const nsA[C]String&| can always be passed a raw character pointer by

 * wrapping it (for free) in a |nsDependent[C]String|.  But a function that

 * takes a character pointer always has the potential to force allocation and

 * copying.

 *

 *

 * How to use it:

 *

 * A |nsPromiseFlat[C]String| doesn't necessarily own the characters it

 * promises.  You must never use it to promise characters out of a string

 * with a shorter lifespan.  The typical use will be something like this:

 *

 *   SomeOSFunction( PromiseFlatCString(aCSubstring).get() ); // GOOD

 *

 * Here's a BAD use:

 *

 *  const char* buffer = PromiseFlatCString(aCSubstring).get();

 *  SomeOSFunction(buffer); // BAD!! |buffer| is a dangling pointer

 *

 * The only way to make one is with the function |PromiseFlat[C]String|,

 * which produce a |const| instance.  ``What if I need to keep a promise

 * around for a little while?'' you might ask.  In that case, you can keep a

 * reference, like so:

 *

 *   const nsCString& flat = PromiseFlatString(aCSubstring);

 *     // Temporaries usually die after the full expression containing the

 *     // expression that created the temporary is evaluated.  But when a

 *     // temporary is assigned to a local reference, the temporary's lifetime

 *     // is extended to the reference's lifetime (C++11 [class.temporary]p5).

 *     //

 *     // This reference holds the anonymous temporary alive.  But remember: it

 *     // must _still_ have a lifetime shorter than that of |aCSubstring|, and

 *     // |aCSubstring| must not be changed while the PromiseFlatString lives.

 *

 *  SomeOSFunction(flat.get());

 *  SomeOtherOSFunction(flat.get());

 *

 *

 * How does it work?

 *

 * A |nsPromiseFlat[C]String| is just a wrapper for another string.  If you

 * apply it to a string that happens to be flat, your promise is just a

 * dependent reference to the string's data.  If you apply it to a non-flat

 * string, then a temporary flat string is created for you, by allocating and

 * copying.  In the event that you end up assigning the result into a sharing

 * string (e.g., |nsTString|), the right thing happens.

 */

template <typename T>

class nsTPromiseFlatString : public nsTString<T>

{

public:

  typedef nsTPromiseFlatString<T> self_type;

  typedef nsTString<T> base_string_type;

  typedef typename base_string_type::substring_type substring_type;

  typedef typename base_string_type::string_type string_type;

  typedef typename base_string_type::substring_tuple_type substring_tuple_type;

  typedef typename base_string_type::char_type char_type;

  typedef typename base_string_type::size_type size_type;

  // These are only for internal use within the string classes:

  typedef typename base_string_type::DataFlags DataFlags;

  typedef typename base_string_type::ClassFlags ClassFlags;

private:

  void Init(const substring_type&);

  // NOT TO BE IMPLEMENTED

  void operator=(const self_type&) = delete;

  // NOT TO BE IMPLEMENTED

  nsTPromiseFlatString() = delete;

  // NOT TO BE IMPLEMENTED

  nsTPromiseFlatString(const string_type& aStr) = delete;

public:

  explicit

  nsTPromiseFlatString(const substring_type& aStr)

    : string_type()

  {

    Init(aStr);

  }

  explicit

  nsTPromiseFlatString(const substring_tuple_type& aTuple)

    : string_type()

  {

    // nothing else to do here except assign the value of the tuple

    // into ourselves.

    this->Assign(aTuple);

  }

};

extern template class nsTPromiseFlatString<char>;

extern template class nsTPromiseFlatString<char16_t>;

// We template this so that the constructor is chosen based on the type of the

// parameter. This allows us to reject attempts to promise a flat flat string.

template<class T>

const nsTPromiseFlatString<T>

TPromiseFlatString(const typename nsTPromiseFlatString<T>::substring_type& aString)

{

  return nsTPromiseFlatString<T>(aString);

}

nsTPromiseFlatString<char> const TPromiseFlatString<char>(nsTPromiseFlatString<char>::substring_type const&)

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Source

128

3.87M

{

129

3.87M

  return nsTPromiseFlatString<T>(aString);

130

3.87M

}

nsTPromiseFlatString<char16_t> const TPromiseFlatString<char16_t>(nsTPromiseFlatString<char16_t>::substring_type const&)

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128

130k

{

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130k

  return nsTPromiseFlatString<T>(aString);

130

130k

}

template<class T>

const nsTPromiseFlatString<T>

TPromiseFlatString(const typename nsTPromiseFlatString<T>::substring_tuple_type& aString)

{

  return nsTPromiseFlatString<T>(aString);

}

Unexecuted instantiation: nsTPromiseFlatString<char> const TPromiseFlatString<char>(nsTPromiseFlatString<char>::substring_tuple_type const&)

Unexecuted instantiation: nsTPromiseFlatString<char16_t> const TPromiseFlatString<char16_t>(nsTPromiseFlatString<char16_t>::substring_tuple_type const&)

#ifndef PromiseFlatCString

#define PromiseFlatCString TPromiseFlatString<char>

#endif

#ifndef PromiseFlatString

#define PromiseFlatString TPromiseFlatString<char16_t>

#endif

#endif