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1 /*
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2 File: FilteringIterator.d
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3
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4 Originally written by Doug Lea and released into the public domain.
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5 Thanks for the assistance and support of Sun Microsystems Labs, Agorics
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6 Inc, Loral, and everyone contributing, testing, and using this code.
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7
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8 History:
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9 Date Who What
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10 22Oct95 dl@cs.oswego.edu Created.
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11
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12 */
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13
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14
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15 module tango.util.collection.iterator.FilteringIterator;
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16
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17 private import tango.core.Exception;
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18
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19 private import tango.util.collection.model.Iterator;
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20
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21 /**
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22 *
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23 * FilteringIterators allow you to filter out elements from
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24 * other enumerations before they are seen by their `consumers'
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25 * (i.e., the callers of `get').
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26 *
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27 * FilteringIterators work as wrappers around other Iterators.
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28 * To build one, you need an existing Iterator (perhaps one
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29 * from coll.elements(), for some Collection coll), and a Predicate
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30 * object (i.e., implementing interface Predicate).
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31 * For example, if you want to screen out everything but Panel
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32 * objects from a collection coll that might hold things other than Panels,
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33 * write something of the form:
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34 * ---
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35 * Iterator e = coll.elements();
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36 * Iterator panels = FilteringIterator(e, IsPanel);
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37 * while (panels.more())
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38 * doSomethingWith(cast(Panel)(panels.get()));
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39 * ---
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40 * To use this, you will also need to write a little class of the form:
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41 * ---
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42 * class IsPanel : Predicate {
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43 * bool predicate(Object v) { return ( 0 !is cast(Panel)v; }
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44 * }
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45 * ---
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46 * See_Also: tango.util.collection.Predicate.predicate
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47 * author: Doug Lea
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48 *
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49 **/
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50
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51 public class FilteringIterator(T) : Iterator!(T)
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52 {
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53 alias bool delegate(T) Predicate;
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54
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55 // instance variables
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56
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57 /**
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58 * The enumeration we are wrapping
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59 **/
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60
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61 private Iterator!(T) src_;
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62
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63 /**
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64 * The screening predicate
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65 **/
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66
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67 private Predicate pred_;
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68
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69 /**
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70 * The sense of the predicate. False means to invert
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71 **/
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72
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73 private bool sign_;
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74
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75 /**
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76 * The next element to hand out
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77 **/
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78
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79 private T get_;
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80
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81 /**
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82 * True if we have a next element
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83 **/
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84
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85 private bool haveNext_;
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86
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87 /**
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88 * Make a Filter using src for the elements, and p as the screener,
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89 * selecting only those elements of src for which p is true
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90 **/
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91
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92 public this (Iterator!(T) src, Predicate p)
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93 {
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94 this(src, p, true);
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95 }
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96
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97 /**
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98 * Make a Filter using src for the elements, and p as the screener,
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99 * selecting only those elements of src for which p.predicate(v) == sense.
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100 * A value of true for sense selects only values for which p.predicate
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101 * is true. A value of false selects only those for which it is false.
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102 **/
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103 public this (Iterator!(T) src, Predicate p, bool sense)
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104 {
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105 src_ = src;
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106 pred_ = p;
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107 sign_ = sense;
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108 findNext();
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109 }
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110
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111 /**
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112 * Implements java.util.Iterator.more
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113 **/
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114
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115 public final bool more()
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116 {
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117 return haveNext_;
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118 }
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119
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120 /**
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121 * Implements java.util.Iterator.get.
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122 **/
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123 public final T get()
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124 {
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125 if (! haveNext_)
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126 throw new NoSuchElementException("exhausted enumeration");
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127 else
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128 {
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129 auto result = get_;
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130 findNext();
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131 return result;
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132 }
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133 }
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134
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135
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136 int opApply (int delegate (inout T value) dg)
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137 {
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138 int result;
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139
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140 while (haveNext_)
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141 {
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142 auto value = get();
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143 if ((result = dg(value)) != 0)
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144 break;
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145 }
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146 return result;
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147 }
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148
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149
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150 /**
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151 * Traverse through src_ elements finding one passing predicate
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152 **/
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153 private final void findNext()
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154 {
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155 haveNext_ = false;
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156
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157 for (;;)
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158 {
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159 if (! src_.more())
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160 return ;
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161 else
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162 {
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163 try {
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164 auto v = src_.get();
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165 if (pred_(v) is sign_)
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166 {
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167 haveNext_ = true;
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168 get_ = v;
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169 return;
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170 }
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171 } catch (NoSuchElementException ex)
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172 {
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173 return;
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174 }
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175 }
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176 }
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177 }
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178 }
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179
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