| 1 | // [License]
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| 2 | // The FreeBSD License
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| 3 | //
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| 4 | // Copyright (c) 2008-2009 Sebastian Mies <mies@edcft.de>
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| 5 | //
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| 6 | // Sebastian Mies
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| 7 | // Gebhardstrasse 25
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| 8 | // 76137 Karlsruhe
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| 9 | // Germany
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| 10 | //
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| 11 | // Redistribution and use in source and binary forms, with or without
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| 12 | // modification, are permitted provided that the following conditions are
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| 13 | // met:
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| 14 | //
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| 15 | // 1. Redistributions of source code must retain the above copyright
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| 16 | // notice, this list of conditions and the following disclaimer.
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| 17 | // 2. Redistributions in binary form must reproduce the above copyright
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| 18 | // notice, this list of conditions and the following disclaimer in the
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| 19 | // documentation and/or other materials provided with the distribution.
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| 20 | //
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| 21 | // THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND
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| 22 | // ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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| 23 | // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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| 24 | // PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS
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| 25 | // BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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| 26 | // EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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| 27 | // PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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| 28 | // PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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| 29 | // LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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| 30 | // NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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| 31 | // SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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| 32 | // [License]
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| 33 |
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| 34 | #ifndef VFACADE_HPP_
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| 35 | #define VFACADE_HPP_
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| 36 |
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| 37 | //--- USAGE INFORMATION --------------------------------------------------------
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| 38 | //
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| 39 | // This header is used to easily implement a virtual facade design pattern. It
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| 40 | // allows to specify a virtual wrapper interface to a non-virtual class. Look
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| 41 | // at this example:
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| 42 | //
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| 43 | // <code>
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| 44 | // // unspecified version
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| 45 | // class to_string_definition : public vfacade_interface {
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| 46 | // public:
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| 47 | // virtual string to_string() const {
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| 48 | // return "UNIMPLEMENTED: to_string()";
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| 49 | // };
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| 50 | // };
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| 51 | //
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| 52 | // // delegation version
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| 53 | // template<class T>
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| 54 | // class vfacade_delegation<to_string_definition, T> :
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| 55 | // public to_string_definition {
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| 56 | // public:
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| 57 | // virtual string to_string() const {
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| 58 | // return get<T>().to_string();
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| 59 | // }
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| 60 | // };
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| 61 | //
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| 62 | // // final type
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| 63 | // typedef vfacade<to_string_definition> vto_string;
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| 64 | // </code>
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| 65 | //
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| 66 | // The to_string_definition specifies an unimplemented facade interface. Its
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| 67 | // necessary for this class not to be pure-virtual. The vfacade_delegation
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| 68 | // specialization implements a delegation any another non-virtual class T.
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| 69 | // Finally the facade type is defined by using the vfacade template. Now,
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| 70 | // we can use this facade, like in the following example:
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| 71 | //
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| 72 | // <code>
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| 73 | // class A {
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| 74 | // public:
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| 75 | // string to_string() {
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| 76 | // return "a hello from class A";
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| 77 | // }
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| 78 | // };
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| 79 | //
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| 80 | // void main() {
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| 81 | // A something;
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| 82 | // vto_string to_str = something;
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| 83 | // cout << to_str->to_string() << endl;
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| 84 | // }
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| 85 | // </code>
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| 86 | //
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| 87 | // This example outputs "a hello from class A" by using the virtual facade. As
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| 88 | // defined class A does not need to know about the facade -- it just implements
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| 89 | // the needed methods. The to_string method is transparently bound to the
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| 90 | // facade by the delegation implementation.
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| 91 | //
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| 92 | // The purpose of this virtual facade is simple: whenever you need a abstract
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| 93 | // representation of non-virtual structures you can simply use a virtual facade.
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| 94 | // It carries a vtable with the delegation to the non-virtual methods and a
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| 95 | // pointer to the original object. Therefore it binds a vtable to a pointer
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| 96 | // so vtable information is stored with the pointer and not with the object
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| 97 | // itself.
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| 98 | //
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| 99 | //------------------------------------------------------------------------------
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| 100 |
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| 101 | // forward declaration
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| 102 | template<class X, class Y>
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| 103 | class vfacade_delegation;
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| 104 |
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| 105 | /**
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| 106 | * This class template implements a virtual facade using a defined interface
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| 107 | * X and a certain delegation specialization of vfascade_delegation<X,Y>.
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| 108 | *
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| 109 | * @author Sebastian Mies <mies@edcft.de>
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| 110 | */
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| 111 | template<class X>
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| 112 | class vfacade {
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| 113 | private:
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| 114 | X value;
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| 115 |
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| 116 | public:
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| 117 | vfacade() {
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| 118 | }
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| 119 |
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| 120 | template<class Y>
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| 121 | vfacade(const Y& _value) {
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| 122 | vfacade_delegation<X, Y> v;
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| 123 | v.set(_value);
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| 124 | memcpy(&value, &v, sizeof(X));
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| 125 | }
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| 126 |
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| 127 | template<class Y>
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| 128 | vfacade<X>& operator=(const Y& _value) {
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| 129 | vfacade_delegation<X, Y> v;
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| 130 | v.set(_value);
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| 131 | memcpy(&value, &v, sizeof(X));
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| 132 | return *this;
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| 133 | }
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| 134 |
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| 135 | vfacade(const vfacade<X>& v) {
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| 136 | memcpy(&value, &v.value, sizeof(X));
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| 137 | }
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| 138 |
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| 139 | vfacade<X>& operator=(const vfacade<X>& v ) {
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| 140 | memcpy(&value, &v.value, sizeof(X));
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| 141 | return *this;
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| 142 | }
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| 143 |
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| 144 | X* operator->() {
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| 145 | return &value;
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| 146 | }
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| 147 |
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| 148 | const X* operator->() const {
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| 149 | return &value;
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| 150 | }
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| 151 | };
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| 152 |
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| 153 | /**
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| 154 | * This class is used as base class for virtual facade interfaces.
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| 155 | *
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| 156 | * @author Sebastian Mies <mies@edcft.de>
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| 157 | */
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| 158 | class vfacade_interface {
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| 159 | template<class X> friend class vfacade;
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| 160 |
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| 161 | private:
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| 162 | void* value;
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| 163 |
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| 164 | protected:
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| 165 | template<class X> X& get() const {
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| 166 | return *((X*) value);
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| 167 | }
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| 168 | template<class X> void set(X& v) {
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| 169 | value = (void*) &v;
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| 170 | }
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| 171 |
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| 172 | public:
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| 173 | vfacade_interface() :
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| 174 | value(NULL) {
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| 175 | }
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| 176 |
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| 177 | bool is_unspecified() const {
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| 178 | return value == NULL;
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| 179 | }
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| 180 |
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| 181 | template<class Y>
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| 182 | Y* ptr() {
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| 183 | return (Y*)value;
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| 184 | }
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| 185 |
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| 186 | template<class Y>
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| 187 | const Y* ptr() const {
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| 188 | return (Y*)value;
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| 189 | }
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| 190 |
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| 191 | template<class Y>
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| 192 | Y& cast_to() {
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| 193 | return *ptr<Y>();
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| 194 | }
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| 195 |
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| 196 | template<class Y>
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| 197 | const Y& cast_to() const {
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| 198 | return *ptr<Y>();
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| 199 | }
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| 200 | };
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| 201 |
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| 202 | /**
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| 203 | * This class is the base template for further delegation specializations.
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| 204 | *
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| 205 | * @author Sebastian Mies <mies@edcft.de>
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| 206 | */
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| 207 | template<class T, class Y>
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| 208 | class vfacade_delegation: public T {
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| 209 |
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| 210 | };
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| 211 |
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| 212 | #endif
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