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96 lines
2.4 KiB
Objective-C
96 lines
2.4 KiB
Objective-C
//------------------------------------------------------------------------------
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/*
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This file is part of Beast: https://github.com/vinniefalco/Beast
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Copyright 2013, Vinnie Falco <vinnie.falco@gmail.com>
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Permission to use, copy, modify, and/or distribute this software for any
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purpose with or without fee is hereby granted, provided that the above
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copyright notice and this permission notice appear in all copies.
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THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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ANY SPECIAL , DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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//==============================================================================
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#ifndef BEAST_SAFEBOOL_H_INCLUDED
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#define BEAST_SAFEBOOL_H_INCLUDED
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namespace beast {
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namespace detail {
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class SafeBoolBase
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{
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private:
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void disallowed () const { }
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public:
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void allowed () const { }
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protected:
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typedef void (SafeBoolBase::*boolean_t) () const;
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SafeBoolBase () { }
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SafeBoolBase (SafeBoolBase const&) { }
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SafeBoolBase& operator= (SafeBoolBase const&)
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{
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return *this;
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}
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~SafeBoolBase () { }
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};
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}
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/** Safe evaluation of class as `bool`.
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This allows a class to be safely evaluated as a bool without the usual
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harmful side effects of the straightforward operator conversion approach.
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To use it, derive your class from SafeBool and implement `asBoolean()` as:
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@code
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bool asBoolean () const;
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@endcode
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Ideas from http://www.artima.com/cppsource/safebool.html
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@class SafeBool
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*/
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template <typename T = void>
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class SafeBool : public detail::SafeBoolBase
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{
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public:
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operator detail::SafeBoolBase::boolean_t () const
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{
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return (static_cast <T const*> (this))->asBoolean ()
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? &SafeBoolBase::allowed : 0;
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}
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protected:
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~SafeBool () { }
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};
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template <typename T, typename U>
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void operator== (SafeBool <T> const& lhs, SafeBool <U> const& rhs)
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{
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lhs.disallowed ();
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}
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template <typename T, typename U>
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void operator!= (SafeBool <T> const& lhs, SafeBool <U> const& rhs)
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{
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lhs.disallowed ();
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}
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}
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#endif
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