| 1 | <HTML
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| 2 | ><HEAD
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| 3 | ><TITLE
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| 4 | >References inside the constructor</TITLE
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| 5 | ><META
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| 6 | NAME="GENERATOR"
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| 7 | CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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| 8 | REL="HOME"
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| 9 | TITLE="Manuál PHP"
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| 10 | HREF="index.html"><LINK
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| 11 | REL="UP"
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| 12 | TITLE="Classes and Objects"
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| 13 | HREF="language.oop.html"><LINK
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| 14 | REL="PREVIOUS"
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| 15 | TITLE="The magic functions __sleep and __wakeup"
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| 16 | HREF="language.oop.magic-functions.html"><LINK
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| 17 | REL="NEXT"
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| 18 | TITLE="Vysvìtlení referencí (odkazù)"
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| 19 | HREF="language.references.html"><META
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| 20 | HTTP-EQUIV="Content-type"
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| 21 | CONTENT="text/html; charset=ISO-8859-2"></HEAD
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| 22 | ><BODY
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| 23 | CLASS="sect1"
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| 24 | BGCOLOR="#FFFFFF"
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| 25 | TEXT="#000000"
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| 26 | LINK="#0000FF"
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| 27 | VLINK="#840084"
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| 28 | ALINK="#0000FF"
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| 29 | ><DIV
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| 30 | CLASS="NAVHEADER"
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| 31 | ><TABLE
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| 32 | SUMMARY="Header navigation table"
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| 33 | WIDTH="100%"
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| 34 | BORDER="0"
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| 35 | CELLPADDING="0"
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| 36 | CELLSPACING="0"
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| 37 | ><TR
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| 38 | ><TH
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| 39 | COLSPAN="3"
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| 40 | ALIGN="center"
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| 41 | >Manuál PHP</TH
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| 42 | ></TR
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| 43 | ><TR
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| 44 | ><TD
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| 45 | WIDTH="10%"
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| 46 | ALIGN="left"
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| 47 | VALIGN="bottom"
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| 48 | ><A
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| 49 | HREF="language.oop.magic-functions.html"
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| 50 | ACCESSKEY="P"
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| 51 | >Pøedcházející</A
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| 52 | ></TD
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| 53 | ><TD
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| 54 | WIDTH="80%"
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| 55 | ALIGN="center"
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| 56 | VALIGN="bottom"
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| 57 | >Kapitola 14. Classes and Objects</TD
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| 58 | ><TD
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| 59 | WIDTH="10%"
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| 60 | ALIGN="right"
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| 61 | VALIGN="bottom"
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| 62 | ><A
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| 63 | HREF="language.references.html"
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| 64 | ACCESSKEY="N"
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| 65 | >Dal¹í</A
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| 66 | ></TD
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| 67 | ></TR
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| 68 | ></TABLE
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| 69 | ><HR
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| 70 | ALIGN="LEFT"
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| 71 | WIDTH="100%"></DIV
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| 72 | ><DIV
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| 73 | CLASS="sect1"
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| 74 | ><H1
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| 75 | CLASS="sect1"
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| 76 | ><A
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| 77 | NAME="language.oop.newref"
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| 78 | ></A
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| 79 | >References inside the constructor</H1
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| 80 | ><P
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| 81 | > Creating references within the constructor can lead to confusing
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| 82 | results. This tutorial-like section helps you to avoid problems.
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| 83 |
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| 84 | <DIV
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| 85 | CLASS="informalexample"
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| 86 | ><A
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| 87 | NAME="AEN5790"
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| 88 | ></A
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| 89 | ><P
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| 90 | ></P
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| 91 | ><TABLE
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| 92 | BORDER="0"
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| 93 | BGCOLOR="#E0E0E0"
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| 94 | CELLPADDING="5"
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| 95 | ><TR
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| 96 | ><TD
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| 97 | ><PRE
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| 98 | CLASS="php"
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| 99 | >class Foo
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| 100 | {
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| 101 | function Foo($name)
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| 102 | {
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| 103 | // create a reference inside the global array $globalref
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| 104 | global $globalref;
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| 105 | $globalref[] = &$this;
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| 106 | // set name to passed value
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| 107 | $this->setName($name);
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| 108 | // and put it out
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| 109 | $this->echoName();
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| 110 | }
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| 111 |
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| 112 | function echoName()
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| 113 | {
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| 114 | echo "<br>",$this->name;
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| 115 | }
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| 116 |
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| 117 | function setName($name)
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| 118 | {
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| 119 | $this->name = $name;
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| 120 | }
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| 121 | }</PRE
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| 122 | ></TD
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| 123 | ></TR
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| 124 | ></TABLE
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| 125 | ><P
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| 126 | ></P
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| 127 | ></DIV
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| 128 | >
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| 129 | </P
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| 130 | ><P
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| 131 | > Let us check out if there is a difference between
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| 132 | <TT
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| 133 | CLASS="varname"
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| 134 | >$bar1</TT
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| 135 | > which has been created using
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| 136 | the copy <TT
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| 137 | CLASS="literal"
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| 138 | >=</TT
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| 139 | > operator and
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| 140 | <TT
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| 141 | CLASS="varname"
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| 142 | >$bar2</TT
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| 143 | > which has been created using
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| 144 | the reference <TT
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| 145 | CLASS="literal"
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| 146 | >=&</TT
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| 147 | > operator...
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| 148 |
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| 149 | <DIV
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| 150 | CLASS="informalexample"
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| 151 | ><A
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| 152 | NAME="AEN5797"
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| 153 | ></A
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| 154 | ><P
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| 155 | ></P
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| 156 | ><TABLE
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| 157 | BORDER="0"
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| 158 | BGCOLOR="#E0E0E0"
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| 159 | CELLPADDING="5"
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| 160 | ><TR
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| 161 | ><TD
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| 162 | ><PRE
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| 163 | CLASS="php"
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| 164 | >$bar1 = new Foo('set in constructor');
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| 165 | $bar1->echoName();
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| 166 | $globalref[0]->echoName();
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| 167 |
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| 168 | /* output:
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| 169 | set in constructor
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| 170 | set in constructor
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| 171 | set in constructor */
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| 172 |
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| 173 | $bar2 =& new Foo('set in constructor');
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| 174 | $bar2->echoName();
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| 175 | $globalref[1]->echoName();
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| 176 |
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| 177 | /* output:
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| 178 | set in constructor
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| 179 | set in constructor
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| 180 | set in constructor */</PRE
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| 181 | ></TD
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| 182 | ></TR
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| 183 | ></TABLE
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| 184 | ><P
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| 185 | ></P
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| 186 | ></DIV
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| 187 | >
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| 188 | </P
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| 189 | ><P
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| 190 | > Apparently there is no difference, but in fact there is a
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| 191 | very significant one: <TT
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| 192 | CLASS="varname"
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| 193 | >$bar1</TT
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| 194 | > and
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| 195 | <TT
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| 196 | CLASS="varname"
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| 197 | >$globalref[0]</TT
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| 198 | > are _NOT_ referenced, they
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| 199 | are NOT the same variable. This is because "new" does not
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| 200 | return a reference by default, instead it returns a copy.
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| 201 | <DIV
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| 202 | CLASS="note"
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| 203 | ><BLOCKQUOTE
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| 204 | CLASS="note"
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| 205 | ><P
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| 206 | ><B
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| 207 | >Poznámka: </B
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| 208 | >
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| 209 | There is no performance loss (since PHP 4 and up use reference
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| 210 | counting) returning copies instead of references. On the
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| 211 | contrary it is most often better to simply work with copies
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| 212 | instead of references, because creating references takes some
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| 213 | time where creating copies virtually takes no time (unless none
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| 214 | of them is a large array or object and one of them gets changed
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| 215 | and the other(s) one(s) subsequently, then it would be wise to
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| 216 | use references to change them all concurrently).
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| 217 | </P
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| 218 | ></BLOCKQUOTE
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| 219 | ></DIV
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| 220 | >
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| 221 | To prove what is written above let us watch the code below.
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| 222 |
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| 223 | <DIV
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| 224 | CLASS="informalexample"
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| 225 | ><A
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| 226 | NAME="AEN5804"
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| 227 | ></A
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| 228 | ><P
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| 229 | ></P
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| 230 | ><TABLE
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| 231 | BORDER="0"
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| 232 | BGCOLOR="#E0E0E0"
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| 233 | CELLPADDING="5"
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| 234 | ><TR
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| 235 | ><TD
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| 236 | ><PRE
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| 237 | CLASS="php"
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| 238 | >// now we will change the name. what do you expect?
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| 239 | // you could expect that both $bar1 and $globalref[0] change their names...
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| 240 | $bar1->setName('set from outside');
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| 241 |
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| 242 | // as mentioned before this is not the case.
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| 243 | $bar1->echoName();
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| 244 | $globalref[0]->echoName();
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| 245 |
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| 246 | /* output:
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| 247 | set from outside
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| 248 | set in constructor */
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| 249 |
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| 250 | // let us see what is different with $bar2 and $globalref[1]
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| 251 | $bar2->setName('set from outside');
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| 252 |
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| 253 | // luckily they are not only equal, they are the same variable
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| 254 | // thus $bar2->name and $globalref[1]->name are the same too
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| 255 | $bar2->echoName();
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| 256 | $globalref[1]->echoName();
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| 257 |
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| 258 | /* output:
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| 259 | set from outside
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| 260 | set from outside */</PRE
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| 261 | ></TD
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| 262 | ></TR
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| 263 | ></TABLE
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| 264 | ><P
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| 265 | ></P
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| 266 | ></DIV
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| 267 | >
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| 268 | </P
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| 269 | ><P
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| 270 | > Another final example, try to understand it.
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| 271 |
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| 272 | <DIV
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| 273 | CLASS="informalexample"
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| 274 | ><A
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| 275 | NAME="AEN5807"
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| 276 | ></A
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| 277 | ><P
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| 278 | ></P
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| 279 | ><TABLE
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| 280 | BORDER="0"
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| 281 | BGCOLOR="#E0E0E0"
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| 282 | CELLPADDING="5"
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| 283 | ><TR
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| 284 | ><TD
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| 285 | ><PRE
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| 286 | CLASS="php"
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| 287 | >class A
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| 288 | {
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| 289 | function A($i)
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| 290 | {
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| 291 | $this->value = $i;
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| 292 | // try to figure out why we do not need a reference here
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| 293 | $this->b = new B($this);
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| 294 | }
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| 295 |
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| 296 | function createRef()
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| 297 | {
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| 298 | $this->c = new B($this);
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| 299 | }
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| 300 |
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| 301 | function echoValue()
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| 302 | {
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| 303 | echo "<br>","class ",get_class($this),': ',$this->value;
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| 304 | }
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| 305 | }
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| 306 |
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| 307 |
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| 308 | class B
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| 309 | {
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| 310 | function B(&$a)
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| 311 | {
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| 312 | $this->a = &$a;
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| 313 | }
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| 314 |
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| 315 | function echoValue()
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| 316 | {
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| 317 | echo "<br>","class ",get_class($this),': ',$this->a->value;
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| 318 | }
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| 319 | }
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| 320 |
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| 321 | // try to undestand why using a simple copy here would yield
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| 322 | // in an undesired result in the *-marked line
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| 323 | $a =& new A(10);
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| 324 | $a->createRef();
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| 325 |
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| 326 | $a->echoValue();
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| 327 | $a->b->echoValue();
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| 328 | $a->c->echoValue();
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| 329 |
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| 330 | $a->value = 11;
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| 331 |
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| 332 | $a->echoValue();
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| 333 | $a->b->echoValue(); // *
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| 334 | $a->c->echoValue();
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| 335 |
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| 336 | /*
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| 337 | output:
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| 338 | class A: 10
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| 339 | class B: 10
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| 340 | class B: 10
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| 341 | class A: 11
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| 342 | class B: 11
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| 343 | class B: 11
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| 344 | */</PRE
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| 345 | ></TD
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| 346 | ></TR
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| 347 | ></TABLE
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| 348 | ><P
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| 349 | ></P
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| 350 | ></DIV
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| 351 | >
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| 352 | </P
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| 353 | ></DIV
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| 354 | ><DIV
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| 355 | CLASS="NAVFOOTER"
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| 356 | ><HR
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| 357 | ALIGN="LEFT"
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| 358 | WIDTH="100%"><TABLE
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| 359 | SUMMARY="Footer navigation table"
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| 360 | WIDTH="100%"
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| 361 | BORDER="0"
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| 362 | CELLPADDING="0"
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| 363 | CELLSPACING="0"
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| 364 | ><TR
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| 365 | ><TD
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| 366 | WIDTH="33%"
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| 367 | ALIGN="left"
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| 368 | VALIGN="top"
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| 369 | ><A
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| 370 | HREF="language.oop.magic-functions.html"
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| 371 | ACCESSKEY="P"
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| 372 | >Pøedcházející</A
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| 373 | ></TD
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| 374 | ><TD
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| 375 | WIDTH="34%"
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| 376 | ALIGN="center"
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| 377 | VALIGN="top"
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| 378 | ><A
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| 379 | HREF="index.html"
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| 380 | ACCESSKEY="H"
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| 381 | >Domù</A
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| 382 | ></TD
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| 383 | ><TD
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| 384 | WIDTH="33%"
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| 385 | ALIGN="right"
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| 386 | VALIGN="top"
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| 387 | ><A
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| 388 | HREF="language.references.html"
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| 389 | ACCESSKEY="N"
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| 390 | >Dal¹í</A
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| 391 | ></TD
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| 392 | ></TR
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| 393 | ><TR
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| 394 | ><TD
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| 395 | WIDTH="33%"
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| 396 | ALIGN="left"
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| 397 | VALIGN="top"
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| 398 | >The magic functions <TT
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| 399 | CLASS="literal"
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| 400 | >__sleep</TT
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| 401 | > and <TT
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| 402 | CLASS="literal"
|
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| 403 | >__wakeup</TT
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| 404 | ></TD
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| 405 | ><TD
|
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| 406 | WIDTH="34%"
|
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| 407 | ALIGN="center"
|
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| 408 | VALIGN="top"
|
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| 409 | ><A
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| 410 | HREF="language.oop.html"
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| 411 | ACCESSKEY="U"
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| 412 | >Nahoru</A
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| 413 | ></TD
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| 414 | ><TD
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| 415 | WIDTH="33%"
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| 416 | ALIGN="right"
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| 417 | VALIGN="top"
|
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| 418 | >Vysvìtlení referencí (odkazù)</TD
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| 419 | ></TR
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| 420 | ></TABLE
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| 421 | ></DIV
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| 422 | ></BODY
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| 423 | ></HTML
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| 424 | >
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