| //// |
| Copyright 1999 Greg Colvin and Beman Dawes |
| Copyright 2002 Darin Adler |
| Copyright 2017 Peter Dimov |
| |
| Distributed under the Boost Software License, Version 1.0. |
| |
| See accompanying file LICENSE_1_0.txt or copy at |
| http://www.boost.org/LICENSE_1_0.txt |
| //// |
| |
| [[history]] |
| [appendix] |
| # History and Acknowledgments |
| :idprefix: history_ |
| |
| ## Summer 1994 |
| |
| Greg Colvin http://www.open-std.org/jtc1/sc22/wg21/docs/papers/1994/N0555.pdf[proposed] |
| to the {cpp} Standards Committee classes named `auto_ptr` and `counted_ptr` which were very |
| similar to what we now call `scoped_ptr` and `shared_ptr`. In one of the very few cases |
| where the Library Working Group's recommendations were not followed by the full committee, |
| `counted_ptr` was rejected and surprising transfer-of-ownership semantics were added to `auto_ptr`. |
| |
| ## October 1998 |
| |
| Beman Dawes proposed reviving the original semantics under the names `safe_ptr` and `counted_ptr`, |
| meeting of Per Andersson, Matt Austern, Greg Colvin, Sean Corfield, Pete Becker, Nico Josuttis, |
| Dietmar Kühl, Nathan Myers, Chichiang Wan and Judy Ward. During the discussion, the four new class |
| names were finalized, it was decided that there was no need to exactly follow the `std::auto_ptr` |
| interface, and various function signatures and semantics were finalized. |
| |
| Over the next three months, several implementations were considered for `shared_ptr`, and discussed |
| on the http://www.boost.org/[boost.org] mailing list. The implementation questions revolved around |
| the reference count which must be kept, either attached to the pointed to object, or detached elsewhere. |
| Each of those variants have themselves two major variants: |
| |
| * Direct detached: the `shared_ptr` contains a pointer to the object, and a pointer to the count. |
| * Indirect detached: the `shared_ptr` contains a pointer to a helper object, which in turn contains a pointer to the object and the count. |
| * Embedded attached: the count is a member of the object pointed to. |
| * Placement attached: the count is attached via operator new manipulations. |
| |
| Each implementation technique has advantages and disadvantages. We went so far as to run various timings |
| of the direct and indirect approaches, and found that at least on Intel Pentium chips there was very little |
| measurable difference. Kevlin Henney provided a paper he wrote on "Counted Body Techniques." Dietmar Kühl |
| suggested an elegant partial template specialization technique to allow users to choose which implementation |
| they preferred, and that was also experimented with. |
| |
| But Greg Colvin and Jerry Schwarz argued that "parameterization will discourage users", and in the end we choose |
| to supply only the direct implementation. |
| |
| ## May 1999 |
| |
| In April and May, 1999, Valentin Bonnard and David Abrahams made a number of suggestions resulting in numerous improvements. |
| |
| ## September 1999 |
| |
| Luis Coelho provided `shared_ptr::swap` and `shared_array::swap`. |
| |
| ## November 1999 |
| |
| Darin Adler provided `operator ==`, `operator !=`, and `std::swap` and `std::less` specializations for shared types. |
| |
| ## May 2001 |
| |
| Vladimir Prus suggested requiring a complete type on destruction. Refinement evolved in discussions including Dave Abrahams, |
| Greg Colvin, Beman Dawes, Rainer Deyke, Peter Dimov, John Maddock, Vladimir Prus, Shankar Sai, and others. |
| |
| ## January 2002 |
| |
| Peter Dimov reworked all four classes, adding features, fixing bugs, splitting them into four separate headers, and adding |
| `weak_ptr`. |
| |
| ## March 2003 |
| |
| Peter Dimov, Beman Dawes and Greg Colvin http://open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html[proposed] `shared_ptr` |
| and `weak_ptr` for inclusion in the Standard Library via the first Library Technical Report (known as TR1). The proposal was |
| accepted and eventually went on to become a part of the {cpp} standard in its 2011 iteration. |
| |
| ## July 2007 |
| |
| Peter Dimov and Beman Dawes http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2351.htm[proposed] a number of enhancements |
| to `shared_ptr` as it was entering the working paper that eventually became the {cpp}11 standard. |
| |
| ## November 2012 |
| |
| Glen Fernandes provided implementations of `make_shared` and `allocate_shared` for arrays. They achieve a single allocation |
| for an array that can be initialized with constructor arguments or initializer lists as well as overloads for default initialization |
| and no value initialization. |
| |
| Peter Dimov aided this development by extending `shared_ptr` to support arrays via the syntax `shared_ptr<T[]>` and `shared_ptr<T[N]>`. |
| |
| ## April 2013 |
| |
| Peter Dimov http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3640.html[proposed] the extension of `shared_ptr` to support |
| arrays for inclusion into the standard, and it was accepted. |
| |
| ## February 2014 |
| |
| Glen Fernandes updated `make_shared` and `allocate_shared` to conform to the specification in {cpp} standard paper |
| http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3870.html[N3870], and implemented `make_unique` for arrays and objects. |
| |
| Peter Dimov and Glen Fernandes updated the scalar and array implementations, respectively, to resolve {cpp} standard library defect 2070. |
| |
| ## February 2017 |
| |
| Glen Fernandes rewrote `allocate_shared` and `make_shared` for arrays for a more optimal and more maintainable implementation. |
| |
| ## June 2017 |
| |
| Peter Dimov and Glen Fernandes rewrote the documentation in Asciidoc format. |
| |
| Peter Dimov added `atomic_shared_ptr` and `local_shared_ptr`. |
| |
| ## August 2019 |
| |
| Glen Fernandes implemented `allocate_unique` for scalars and arrays. |