[ARX程序]：Cool helper classes for ARX part 2: ARX goes STL

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2. 
   
3. Cool helper classes for ARX part 2: ARX goes STL  
   
4. ID    1696  
   
5. Applies to:    AutoCAD 2000I
   
6. AutoCAD 2002
   
7. AutoCAD 2000
   
8. 
   
9. Date    1/22/2002  
   
10. 
    
11. This document is part of    AutoCAD Utilities     
    
12. 
    
13. 
    
14. Question
    
15. This solution is an extension of the helper classes presented in <Solution 1695>
    
16. "ACAD: COOL HELPER CLASSES FOR ARX" which is a prerequisite for this solution
    
17. and should be looked at first.
    
18. Answer
    
19. I generalized the template class Apply even more, which now works only with
    
20. MSVC 6.0 now, as I'm using template member functions in template classes.)
    
21. 
    
22. Up to now (version 1), Apply took a function pointer as an argument for the
    
23. constructor. This function pointer had to be a pointer to a function that takes
    
24. one argument.
    
25. 
    
26. Now (version 2), Apply takes a template parameter as argument for the constructor.
    
27. Valid is everything that can be applied a '()' operation on. This CAN be - of
    
28. course - a function pointer, like before. But it also can be a class object
    
29. of a class with in overloaded '()' operator.
    
30. 
    
31. You can do really cool things with it. For example, I wanted to have an apply
    
32. function which takes not only one argument, as in ...
    
33. 
    
34. 
    
35. Adesk::Boolean applyFunc( AcDbEntity * );
    
36. 
    
37. ... but two arguments, as in ...
    
38. 
    
39. 
    
40. Adesk::Boolean transform( AcDbEntity *p, const AcGeMatrix3d& m )
    
41. {
    
42.     p->transformBy( m );
    
43.     return Adesk::kTrue;
    
44. }
    
45. 
    
46. ... because I wanted to apply an user-supplied transformation matrix to each
    
47. entity in a block.
    
48. 
    
49. Instead of modifying the Apply class (which is what I didn't want to do because
    
50. I wanted to keep this class as minimal as possible), you can solve this entirely
    
51. by using Template helper classes and -functions.
    
52. 
    
53. The name of the first template helper class is '_2', which makes it possible
    
54. to apply a function that takes two arguments.
    
55. 
    
56. The calling syntax is:
    
57. 
    
58. 
    
59. AcGeMatrix3d mat;
    
60.      mat.setToTranslation( AcGeVector3d( 5.0, 2.0, 0.0 ) );
    
61.      Apply<BlockTableRecord>( pMs, _2( transform, mat ), kForWrite );
    
62. 
    
63. Now how does this work?
    
64. 
    
65. _2 has a constructor which takes two template arguments. (transform and mat).
    
66. The constructor just stores these two objects as data members. Now comes the
    
67. trick: _2 has an overloaded '()' operator, which takes one argument; because
    
68. this is exactly what apply needs. The operator '()' in turn just calls it's
    
69. constructor's argument #1, passing the constructor's argument #2 as an additional
    
70. argument to the apply function (argument #1).
    
71. 
    
72. Sample code:
    
73. 
    
74. 
    
75. _2::_2( T t, S s ) : m_t( t ), m_s( s ) { }
    
76. 
    
77. Adesk::Boolean _2::operator () (P* pEnt)
    
78. {  return m_t( pEnt, s );  }
    
79. 
    
80. That's it. It's really as simple as this. Still reading? :-)
    
81. 
    
82. Another neat template helper class is 'If'. The If constructor takes (again)
    
83. two arguments: the first one is a filter function, and the second one is the
    
84. apply function. The apply function will be called only if a specific object
    
85. passes the filter function. If you consider the following filter function:
    
86. 
    
87. 
    
88. Adesk::Boolean isAcDbLine( AcDbEntity *pEnt )
    
89. {
    
90.     return pEnt->isKindOf( AcDbLine::desc() );
    
91. }
    
92. 
    
93. ... then the calling sequence
    
94. 
    
95. 
    
96. Apply<BlockTableRecord>( pMs,
    
97. If( isAcDbLine, applyFunc ), kForRead );
    
98. ... calls applyFunc() only if the entity is an AcDbLine. The implementation
    
99. of If is similar to _2:
    
100. 
     
101. 
     
102. If::If( T t, S s ) : m_t( t ), m_s( s ) { }
     
103. 
     
104. Adesk::Boolean If::operator () (P* pEnt)
     
105. {  return m_s( pEnt ) ? m_t( pEnt ) : Adesk::kTrue;  }
     
106. 
     
107. This code above calls the apply function (m_t) only if the object passes the
     
108. filter (m_s). This means, the following code:
     
109. 
     
110. 
     
111. Apply<BlockTableRecord>( pMs,
     
112.          If( isAcDbLine, applyFunc ), kForRead );
     
113. 
     
114. ... causes that applyFunc() is called for each Line in the model space. Of course,
     
115. you can combine these two classes, as in:
     
116. 
     
117. 
     
118. Apply<BlockTableRecord>( pMs,
     
119.          If( isAcDbLine, _2( transform, mat ) ), kForWrite );
     
120. 
     
121. This applies the transformation matrix 'mat' to each line in model space. But
     
122. the first parameter to If (the filter function) is also templatized, so it can
     
123. also be a class object instead of a function pointer. Which means: taken the
     
124. following filter function (note that this one also takes TWO arguments [you
     
125. guess what happens...?]):
     
126. 
     
127. 
     
128. Adesk::Boolean hasColor( AcDbEntity *pEnt, int color )
     
129. {
     
130.     return pEnt->colorIndex() == color;
     
131. }
     
132. 
     
133. ..., if you use this like the following:
     
134. 
     
135. 
     
136. Apply<BlockTableRecord>( pMs,
     
137.          If( _2( hasColor, 4 ), _2( transform, mat ) ), kForWrite );
     
138. 
     
139. ... causes each entity in model space with the colorIndex of 4 to be translated
     
140. by 'mat'. On the other hand,
     
141. 
     
142. 
     
143. Apply<BlockTableRecord>( pMs,
     
144.          If( _2( hasColor, 6 ), _2( transform, mat2 ) ), kForWrite );
     
145. 
     
146. ... will apply the matrix 'mat2' to each entity with the colorIndex of 6.
     
147. 
     
148. Is this flexible? Is this cool? Or what?
     
149. 
     
150. All this is done by only a few lines of code. Just a few minimal template classes:
     
151. Apply, Filter and TwoArgs. It's completely customizable and extendible by users
     
152. of these classes. (You can add helpers for functions with three parameters,
     
153. and so on.) You can apply every complex operation you want on every object with
     
154. every imaginable search-criteria in the database. Needless to say, Apply doesn't
     
155. work only with entities, it works also with Dictionaries, and all other symbol tables.
     
156. 
     
157. There's really no limit for improvements. Be creative! For example, the function
     
158. 'isAcDbLine( AcDbEntity *pEnt )' above can be generalized to 'isKindOf( AcDbObject
     
159. *pObj, AcRxClass *desc )', so the term
     
160. 
     
161. 
     
162. Apply<BlockTableRecord>( pMs,
     
163.      If( isAcDbLine, testFunc1 ), kForRead );
     
164. 
     
165. ... can be also be formulated as ...
     
166. 
     
167. 
     
168. Apply<BlockTableRecord>( pMs,
     
169.      If( _2( isKindOf, AcDbLine::desc() ), testFunc1 ), kForRead );
     
170. 
     
171. Or, what about two more classes 'And' and 'Or', which apply the following operation
     
172. on their two parameters:
     
173. 
     
174. 
     
175. Adesk::Boolean And::operator () ( P* p)
     
176.     { return m_t( p ) && m_s( p ); }
     
177. 
     
178.     Adesk::Boolean Or::operator () ( P* p)
     
179.     { return m_t( p ) || m_s( p ); }
     
180. 
     
181. ... so you can use them as boolean operations for the Apply class:
     
182. 
     
183. 
     
184. Apply<BlockTableRecord>( pMs,
     
185.          If( Or( _2( isKindOf, AcDbLine::desc() ),
     
186.              _2( isKindOf, AcDbCircle::desc() ) ),
     
187.          _2( transform, mat ) ),
     
188.          kForWrite );
     
189. 
     
190. This code above will apply the transformation matrix 'mat' to all circles and
     
191. lines in the model space, while ...
     
192. 
     
193. 
     
194. Apply<BlockTableRecord>( pMs,
     
195.          If( And( _2( isColor, 3 ),
     
196.               _2( isKindOf, AcDbCircle::desc() ) ),
     
197.          _2( transform, mat ) ),
     
198.          kForWrite );
     
199. 
     
200. ... will apply 'mat' only to all circles with the color 3.
     
201. 
     
202. If you're familiar with STL (the Standard Template Library), then the code presented
     
203. here will be familiar to you as well: this is *exactly* how STL works. I mean,
     
204. applying generic functions to all sort of containers, with all sort of combinations.
     
205. 
     
206. Full source code is attached.
     

<br /> Cool helper classes for ARX part 2: ARX goes STL  <br /> ID    1696  <br /> Applies to:    AutoCAD 2000I<br /> AutoCAD 2002<br /> AutoCAD 2000<br /> <br /> Date    1/22/2002  <br /> <br /> This document is part of    AutoCAD Utilities     <br /> <br /> <br /> Question <br /> This solution is an extension of the helper classes presented in <Solution 1695> <br /> "ACAD: COOL HELPER CLASSES FOR ARX" which is a prerequisite for this solution <br /> and should be looked at first.<br /> Answer <br /> I generalized the template class Apply even more, which now works only with <br /> MSVC 6.0 now, as I'm using template member functions in template classes.)<br /> <br /> Up to now (version 1), Apply took a function pointer as an argument for the <br /> constructor. This function pointer had to be a pointer to a function that takes <br /> one argument.<br /> <br /> Now (version 2), Apply takes a template parameter as argument for the constructor. <br /> Valid is everything that can be applied a '()' operation on. This CAN be - of <br /> course - a function pointer, like before. But it also can be a class object <br /> of a class with in overloaded '()' operator.<br /> <br /> You can do really cool things with it. For example, I wanted to have an apply <br /> function which takes not only one argument, as in ...<br /> <br /> <br /> Adesk::Boolean applyFunc( AcDbEntity * );<br /> <br /> ... but two arguments, as in ...<br /> <br /> <br /> Adesk::Boolean transform( AcDbEntity *p, const AcGeMatrix3d& m )<br /> {<br />     p->transformBy( m );<br />     return Adesk::kTrue;<br /> }<br /> <br /> ... because I wanted to apply an user-supplied transformation matrix to each <br /> entity in a block.<br /> <br /> Instead of modifying the Apply class (which is what I didn't want to do because <br /> I wanted to keep this class as minimal as possible), you can solve this entirely <br /> by using Template helper classes and -functions.<br /> <br /> The name of the first template helper class is '_2', which makes it possible <br /> to apply a function that takes two arguments.<br /> <br /> The calling syntax is:<br /> <br /> <br /> AcGeMatrix3d mat;<br />      mat.setToTranslation( AcGeVector3d( 5.0, 2.0, 0.0 ) );<br />      Apply<BlockTableRecord>( pMs, _2( transform, mat ), kForWrite );<br /> <br /> Now how does this work?<br /> <br /> _2 has a constructor which takes two template arguments. (transform and mat). <br /> The constructor just stores these two objects as data members. Now comes the <br /> trick: _2 has an overloaded '()' operator, which takes one argument; because <br /> this is exactly what apply needs. The operator '()' in turn just calls it's <br /> constructor's argument #1, passing the constructor's argument #2 as an additional <br /> argument to the apply function (argument #1).<br /> <br /> Sample code:<br /> <br /> <br /> _2::_2( T t, S s ) : m_t( t ), m_s( s ) { }<br /> <br /> Adesk::Boolean _2::operator () (P* pEnt)<br /> {  return m_t( pEnt, s );  }<br /> <br /> That's it. It's really as simple as this. Still reading? :-)<br /> <br /> Another neat template helper class is 'If'. The If constructor takes (again) <br /> two arguments: the first one is a filter function, and the second one is the <br /> apply function. The apply function will be called only if a specific object <br /> passes the filter function. If you consider the following filter function:<br /> <br /> <br /> Adesk::Boolean isAcDbLine( AcDbEntity *pEnt )<br /> {<br />     return pEnt->isKindOf( AcDbLine::desc() );<br /> }<br /> <br /> ... then the calling sequence<br /> <br /> <br /> Apply<BlockTableRecord>( pMs,<br /> If( isAcDbLine, applyFunc ), kForRead );<br /> ... calls applyFunc() only if the entity is an AcDbLine. The implementation <br /> of If is similar to _2:<br /> <br /> <br /> If::If( T t, S s ) : m_t( t ), m_s( s ) { }<br /> <br /> Adesk::Boolean If::operator () (P* pEnt)<br /> {  return m_s( pEnt ) ? m_t( pEnt ) : Adesk::kTrue;  }<br /> <br /> This code above calls the apply function (m_t) only if the object passes the <br /> filter (m_s). This means, the following code:<br /> <br /> <br /> Apply<BlockTableRecord>( pMs,<br />          If( isAcDbLine, applyFunc ), kForRead );<br /> <br /> ... causes that applyFunc() is called for each Line in the model space. Of course, <br /> you can combine these two classes, as in:<br /> <br /> <br /> Apply<BlockTableRecord>( pMs,<br />          If( isAcDbLine, _2( transform, mat ) ), kForWrite );<br /> <br /> This applies the transformation matrix 'mat' to each line in model space. But <br /> the first parameter to If (the filter function) is also templatized, so it can <br /> also be a class object instead of a function pointer. Which means: taken the <br /> following filter function (note that this one also takes TWO arguments [you <br /> guess what happens...?]):<br /> <br /> <br /> Adesk::Boolean hasColor( AcDbEntity *pEnt, int color )<br /> {<br />     return pEnt->colorIndex() == color;<br /> }<br /> <br /> ..., if you use this like the following:<br /> <br /> <br /> Apply<BlockTableRecord>( pMs,<br />          If( _2( hasColor, 4 ), _2( transform, mat ) ), kForWrite );<br /> <br /> ... causes each entity in model space with the colorIndex of 4 to be translated <br /> by 'mat'. On the other hand,<br /> <br /> <br /> Apply<BlockTableRecord>( pMs,<br />          If( _2( hasColor, 6 ), _2( transform, mat2 ) ), kForWrite );<br /> <br /> ... will apply the matrix 'mat2' to each entity with the colorIndex of 6.<br /> <br /> Is this flexible? Is this cool? Or what?<br /> <br /> All this is done by only a few lines of code. Just a few minimal template classes: <br /> Apply, Filter and TwoArgs. It's completely customizable and extendible by users <br /> of these classes. (You can add helpers for functions with three parameters, <br /> and so on.) You can apply every complex operation you want on every object with <br /> every imaginable search-criteria in the database. Needless to say, Apply doesn't <br /> work only with entities, it works also with Dictionaries, and all other symbol tables.<br /> <br /> There's really no limit for improvements. Be creative! For example, the function <br /> 'isAcDbLine( AcDbEntity *pEnt )' above can be generalized to 'isKindOf( AcDbObject <br /> *pObj, AcRxClass *desc )', so the term<br /> <br /> <br /> Apply<BlockTableRecord>( pMs,<br />      If( isAcDbLine, testFunc1 ), kForRead );<br /> <br /> ... can be also be formulated as ...<br /> <br /> <br /> Apply<BlockTableRecord>( pMs,<br />      If( _2( isKindOf, AcDbLine::desc() ), testFunc1 ), kForRead );<br /> <br /> Or, what about two more classes 'And' and 'Or', which apply the following operation <br /> on their two parameters:<br /> <br /> <br /> Adesk::Boolean And::operator () ( P* p)<br />     { return m_t( p ) && m_s( p ); }<br /> <br />     Adesk::Boolean Or::operator () ( P* p)<br />     { return m_t( p ) || m_s( p ); }<br /> <br /> ... so you can use them as boolean operations for the Apply class:<br /> <br /> <br /> Apply<BlockTableRecord>( pMs,<br />          If( Or( _2( isKindOf, AcDbLine::desc() ),<br />              _2( isKindOf, AcDbCircle::desc() ) ),<br />          _2( transform, mat ) ),<br />          kForWrite );<br /> <br /> This code above will apply the transformation matrix 'mat' to all circles and <br /> lines in the model space, while ...<br /> <br /> <br /> Apply<BlockTableRecord>( pMs,<br />          If( And( _2( isColor, 3 ),<br />               _2( isKindOf, AcDbCircle::desc() ) ),<br />          _2( transform, mat ) ),<br />          kForWrite );<br /> <br /> ... will apply 'mat' only to all circles with the color 3.<br /> <br /> If you're familiar with STL (the Standard Template Library), then the code presented <br /> here will be familiar to you as well: this is *exactly* how STL works. I mean, <br /> applying generic functions to all sort of containers, with all sort of combinations.<br /> <br /> Full source code is attached.<br />