forked from boostorg/smart_ptr
90 lines
4.2 KiB
Plaintext
90 lines
4.2 KiB
Plaintext
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Copyright 1999 Greg Colvin and Beman Dawes
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Copyright 2002 Darin Adler
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Copyright 2017 Peter Dimov
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Distributed under the Boost Software License, Version 1.0.
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See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt
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////
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[appendix,#history]
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# History and Acknowledgments
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:idprefix:
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## Summer 1994
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Greg Colvin http://www.open-std.org/jtc1/sc22/wg21/docs/papers/1994/N0555.pdf[proposed]
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to the {cpp} Standards Committee classes named `auto_ptr` and `counted_ptr` which were very
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similar to what we now call `scoped_ptr` and `shared_ptr`. In one of the very few cases
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where the Library Working Group's recommendations were not followed by the full committee,
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`counted_ptr` was rejected and surprising transfer-of-ownership semantics were added to `auto_ptr`.
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## October 1998
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Beman Dawes proposed reviving the original semantics under the names `safe_ptr` and `counted_ptr`,
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meeting of Per Andersson, Matt Austern, Greg Colvin, Sean Corfield, Pete Becker, Nico Josuttis,
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Dietmar Kühl, Nathan Myers, Chichiang Wan and Judy Ward. During the discussion, the four new class
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names were finalized, it was decided that there was no need to exactly follow the `std::auto_ptr`
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interface, and various function signatures and semantics were finalized.
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Over the next three months, several implementations were considered for `shared_ptr`, and discussed
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on the http://www.boost.org/[boost.org] mailing list. The implementation questions revolved around
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the reference count which must be kept, either attached to the pointed to object, or detached elsewhere.
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Each of those variants have themselves two major variants:
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* Direct detached: the `shared_ptr` contains a pointer to the object, and a pointer to the count.
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* Indirect detached: the `shared_ptr` contains a pointer to a helper object, which in turn contains a pointer to the object and the count.
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* Embedded attached: the count is a member of the object pointed to.
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* Placement attached: the count is attached via operator new manipulations.
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Each implementation technique has advantages and disadvantages. We went so far as to run various timings
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of the direct and indirect approaches, and found that at least on Intel Pentium chips there was very little
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measurable difference. Kevlin Henney provided a paper he wrote on "Counted Body Techniques." Dietmar Kühl
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suggested an elegant partial template specialization technique to allow users to choose which implementation
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they preferred, and that was also experimented with.
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But Greg Colvin and Jerry Schwarz argued that "parameterization will discourage users", and in the end we choose
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to supply only the direct implementation.
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## May 1999
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In April and May, 1999, Valentin Bonnard and David Abrahams made a number of suggestions resulting in numerous improvements.
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## September 1999
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Luis Coelho provided `shared_ptr::swap` and `shared_array::swap`.
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## November 1999
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Darin Adler provided `operator ==`, `operator !=`, and `std::swap` and `std::less` specializations for shared types.
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## May 2001
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Vladimir Prus suggested requiring a complete type on destruction. Refinement evolved in discussions including Dave Abrahams,
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Greg Colvin, Beman Dawes, Rainer Deyke, Peter Dimov, John Maddock, Vladimir Prus, Shankar Sai, and others.
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## January 2002
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Peter Dimov reworked all four classes, adding features, fixing bugs, splitting them into four separate headers, and adding
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`weak_ptr`.
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## November 2012
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Glen Fernandes provided implementations of `make_shared` and `allocate_shared` for arrays. They achieve a single allocation
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for an array that can be initialized with constructor arguments or initializer lists as well as overloads for default initialization
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and no value initialization.
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## February 2014
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Glen Fernandes updated overloads of `make_shared` and `allocate_shared` to conform to the specification in {cpp} standard paper
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http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3870.html[N3870],
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and implemented `make_unique` for arrays and objects. Peter Dimov and Glen Fernandes updated the scalar and array implementations,
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respectively, to resolve {cpp} standard library defect 2070.
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## February 2017
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Glen Fernandes rewrote `allocate_shared` and `make_shared` for arrays for a more optimal and more maintainable implementation.
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