mirror of
https://github.com/classilla/tenfourfox.git
synced 2024-09-09 04:54:33 +00:00
113 lines
4.0 KiB
C++
113 lines
4.0 KiB
C++
/* -*- 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/. */
|
|
|
|
|
|
/**
|
|
* 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.
|
|
*/
|
|
|
|
class nsTPromiseFlatString_CharT : public nsTString_CharT
|
|
{
|
|
public:
|
|
|
|
typedef nsTPromiseFlatString_CharT self_type;
|
|
|
|
private:
|
|
|
|
void Init(const substring_type&);
|
|
|
|
// NOT TO BE IMPLEMENTED
|
|
void operator=(const self_type&) = delete;
|
|
|
|
// NOT TO BE IMPLEMENTED
|
|
nsTPromiseFlatString_CharT() = delete;
|
|
|
|
// NOT TO BE IMPLEMENTED
|
|
nsTPromiseFlatString_CharT(const string_type& aStr) = delete;
|
|
|
|
public:
|
|
|
|
explicit
|
|
nsTPromiseFlatString_CharT(const substring_type& aStr)
|
|
: string_type()
|
|
{
|
|
Init(aStr);
|
|
}
|
|
|
|
explicit
|
|
nsTPromiseFlatString_CharT(const substring_tuple_type& aTuple)
|
|
: string_type()
|
|
{
|
|
// nothing else to do here except assign the value of the tuple
|
|
// into ourselves.
|
|
Assign(aTuple);
|
|
}
|
|
};
|
|
|
|
// 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_CharT
|
|
TPromiseFlatString_CharT(const T& aString)
|
|
{
|
|
return nsTPromiseFlatString_CharT(aString);
|
|
}
|