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1 /*
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2 File: InterleavingIterator.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.InterleavingIterator;
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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 * InterleavingIterators allow you to combine the elements
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24 * of two different enumerations as if they were one enumeration
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25 * before they are seen by their `consumers'.
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26 * This sometimes allows you to avoid having to use a
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27 * Collection object to temporarily combine two sets of Collection elements()
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28 * that need to be collected together for common processing.
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29 * <P>
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30 * The elements are revealed (via get()) in a purely
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31 * interleaved fashion, alternating between the first and second
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32 * enumerations unless one of them has been exhausted, in which case
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33 * all remaining elements of the other are revealed until it too is
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34 * exhausted.
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35 * <P>
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36 * InterleavingIterators work as wrappers around other Iterators.
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37 * To build one, you need two existing Iterators.
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38 * For example, if you want to process together the elements of
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39 * two Collections a and b, you could write something of the form:
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40 * <PRE>
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41 * Iterator items = InterleavingIterator(a.elements(), b.elements());
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42 * while (items.more())
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43 * doSomethingWith(items.get());
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44 * </PRE>
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45 *
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46 author: Doug Lea
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47 * @version 0.93
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48 *
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49 * <P> For an introduction to this package see <A HREF="index.html"> Overview </A>.
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50 *
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51 **/
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52
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53
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54 public class InterleavingIterator(T) : Iterator!(T)
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55 {
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56
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57 /**
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58 * The first source; nulled out once it is exhausted
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59 **/
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60
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61 private Iterator!(T) fst_;
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62
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63 /**
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64 * The second source; nulled out once it is exhausted
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65 **/
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66
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67 private Iterator!(T) snd_;
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68
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69 /**
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70 * The source currently being used
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71 **/
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72
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73 private Iterator!(T) current_;
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74
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75
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76
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77 /**
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78 * Make an enumeration interleaving elements from fst and snd
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79 **/
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80
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81 public this (Iterator!(T) fst, Iterator!(T) snd)
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82 {
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83 fst_ = fst;
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84 snd_ = snd;
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85 current_ = snd_; // flip will reset to fst (if it can)
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86 flip();
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87 }
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88
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89 /**
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90 * Implements java.util.Iterator.more
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91 **/
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92 public final bool more()
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93 {
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94 return current_ !is null;
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95 }
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96
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97 /**
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98 * Implements java.util.Iterator.get.
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99 **/
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100 public final T get()
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101 {
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102 if (current_ is null)
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103 throw new NoSuchElementException("exhausted iterator");
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104 else
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105 {
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106 // following line may also throw ex, but there's nothing
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107 // reasonable to do except propagate
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108 auto result = current_.get();
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109 flip();
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110 return result;
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111 }
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112 }
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113
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114
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115 int opApply (int delegate (inout T value) dg)
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116 {
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117 int result;
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118
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119 while (current_)
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120 {
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121 auto value = get();
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122 if ((result = dg(value)) != 0)
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123 break;
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124 }
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125 return result;
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126 }
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127
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128 /**
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129 * Alternate sources
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130 **/
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131
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132 private final void flip()
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133 {
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134 if (current_ is fst_)
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135 {
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136 if (snd_ !is null && !snd_.more())
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137 snd_ = null;
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138 if (snd_ !is null)
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139 current_ = snd_;
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140 else
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141 {
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142 if (fst_ !is null && !fst_.more())
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143 fst_ = null;
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144 current_ = fst_;
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145 }
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146 }
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147 else
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148 {
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149 if (fst_ !is null && !fst_.more())
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150 fst_ = null;
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151 if (fst_ !is null)
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152 current_ = fst_;
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153 else
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154 {
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155 if (snd_ !is null && !snd_.more())
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156 snd_ = null;
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157 current_ = snd_;
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158 }
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159 }
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160 }
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161
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162
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163 }
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164
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