ch13_15.htm

来自「By Tom Christiansen and Nathan Torkingto」· HTM 代码 · 共 793 行 · 第 1/2 页

} 

# this uses stringify
sub concat { 
    my ($s1, $s2, $inverted) = @_;
    return StrNum $inverted ? ($s2 . $s1) : ($s1 . $s2);

} 

# this uses stringify
sub repeat { 
    my ($s1, $s2, $inverted) = @_;
    return StrNum $inverted ? ($s2 x $s1) : ($s1 x $s2);
}

1;<A
CLASS="indexterm"
NAME="ch13-idx-1000005577-0"
></A
><A
CLASS="indexterm"
NAME="ch13-idx-1000005577-1"
></A
></PRE
></DIV
></DIV
><DIV
CLASS="sect2"
><H3
CLASS="sect2"
><A
CLASS="title"
NAME="ch13-16506"
>Example: Overloaded FixNum Class</A
></H3
><P
CLASS="para"
><A
CLASS="indexterm"
NAME="ch13-idx-1000006591-0"
></A
><A
CLASS="indexterm"
NAME="ch13-idx-1000006591-1"
></A
><A
CLASS="indexterm"
NAME="ch13-idx-1000006591-2"
></A
><A
CLASS="indexterm"
NAME="ch13-idx-1000006591-3"
></A
><A
CLASS="indexterm"
NAME="ch13-idx-1000006591-4"
></A
>This class uses operator overloading to control the number of decimal places in output. It still uses full precision for its operations. A <CODE
CLASS="literal"
>places()</CODE
> method can be used on the class or a particular object to set the number of places of output to the right of the decimal point.</P
><PRE
CLASS="programlisting"
>#!/usr/bin/perl
# demo_fixnum - show operator overloading
use FixNum;

FixNum-&gt;places(5);

$x = FixNum-&gt;new(40);
$y = FixNum-&gt;new(12);

print &quot;sum of $x and $y is &quot;, $x + $y, &quot;\n&quot;;
print &quot;product of $x and $y is &quot;, $x * $y, &quot;\n&quot;;

$z = $x / $y;
printf &quot;$z has %d places\n&quot;, $z-&gt;places;
$z-&gt;places(2) unless $z-&gt;places;
print &quot;div of $x by $y is $z\n&quot;;
print &quot;square of that is &quot;, $z * $z, &quot;\n&quot;;

<CODE
CLASS="userinput"
><B
><CODE
CLASS="replaceable"
><I
>sum of STRFixNum: 40 and STRFixNum: 12 is STRFixNum: 52</I
></CODE
></B
></CODE
>
<CODE
CLASS="userinput"
><B
><CODE
CLASS="replaceable"
><I
>product of STRFixNum: 40 and STRFixNum: 12 is STRFixNum: 480</I
></CODE
></B
></CODE
>
<CODE
CLASS="userinput"
><B
><CODE
CLASS="replaceable"
><I
>STRFixNum: 3 has 0 places</I
></CODE
></B
></CODE
>
<CODE
CLASS="userinput"
><B
><CODE
CLASS="replaceable"
><I
>div of STRFixNum: 40 by STRFixNum: 12 is STRFixNum: 3.33</I
></CODE
></B
></CODE
>
<CODE
CLASS="userinput"
><B
><CODE
CLASS="replaceable"
><I
>square of that is STRFixNum: 11.11</I
></CODE
></B
></CODE
></PRE
><P
CLASS="para"
>The class itself is shown in <A
CLASS="xref"
HREF="ch13_15.htm#ch13-16079"
TITLE="FixNum"
>Example 13.2</A
>. It only overloads the addition, multiplication, and division operations for math operators. Other operators are the spaceship operator, which handles all comparisons, the string-interpolation operator, and the numeric conversion operator. The string interpolation operator is given a distinctive look for debugging purposes.</P
><DIV
CLASS="example"
><H4
CLASS="example"
><A
CLASS="title"
NAME="ch13-16079"
>Example 13.2: FixNum</A
></H4
><PRE
CLASS="programlisting"
>package FixNum;

use strict;

my $PLACES = 0;

sub new {
    my $proto   = shift;
    my $class   = ref($proto) || $proto;
    my $parent  = ref($proto) &amp;&amp; $proto;

    my $v = shift;
    my $self = {
        VALUE  =&gt; $v,
        PLACES =&gt; undef,
    }; 
    if ($parent &amp;&amp; defined $parent-&gt;{PLACES}) {
        $self-&gt;{PLACES} = $parent-&gt;{PLACES};
    } elsif ($v =~ /(\.\d*)/) {
        $self-&gt;{PLACES} = length($1) - 1;
    }  else {
        $self-&gt;{PLACES} = 0;
    } 
    return bless $self, $class;
} 

sub places {
    my $proto = shift;
    my $self  = ref($proto) &amp;&amp; $proto;
    my $type  = ref($proto) || $proto;

    if (@_) {
        my $places = shift;
        ($self ? $self-&gt;{PLACES} : $PLACES) = $places;
    } 
    return $self ? $self-&gt;{PLACES} : $PLACES;
} 

sub _max { $_[0] &gt; $_[1] ? $_[0] : $_[1] } 

use overload '+'    =&gt; \&amp;add,
             '*'    =&gt; \&amp;multiply,
             '/'    =&gt; \&amp;divide,
             '&lt;=&gt;'  =&gt; \&amp;spaceship,
             '&quot;&quot;'   =&gt; \&amp;as_string,
             '0+'   =&gt; \&amp;as_number;

sub add {
    my ($this, $that, $flipped) = @_;
    my $result = $this-&gt;new( $this-&gt;{VALUE} + $that-&gt;{VALUE} );
    $result-&gt;places( _max($this-&gt;{PLACES}, $that-&gt;{PLACES} ));
    return $result;
} 

sub multiply {
    my ($this, $that, $flipped) = @_;
    my $result = $this-&gt;new( $this-&gt;{VALUE} * $that-&gt;{VALUE} );
    $result-&gt;places( _max($this-&gt;{PLACES}, $that-&gt;{PLACES} ));
    return $result;
} 

sub divide {
    my ($this, $that, $flipped) = @_;
    my $result = $this-&gt;new( $this-&gt;{VALUE} / $that-&gt;{VALUE} );
    $result-&gt;places( _max($this-&gt;{PLACES}, $that-&gt;{PLACES} ));
    return $result;
} 

sub as_string {
    my $self = shift;
    return sprintf(&quot;STR%s: %.*f&quot;, ref($self), 
        defined($self-&gt;{PLACES}) ? $self-&gt;{PLACES} : $PLACES,
            $self-&gt;{VALUE}); 
} 

sub as_number {
    my $self = shift;
    return $self-&gt;{VALUE};
} 
    
sub spaceship {
    my ($this, $that, $flipped) = @_;
    $this-&gt;{VALUE} &lt;=&gt; $that-&gt;{VALUE};
} 
<A
CLASS="indexterm"
NAME="ch13-idx-1000005805-0"
></A
><A
CLASS="indexterm"
NAME="ch13-idx-1000005805-1"
></A
><A
CLASS="indexterm"
NAME="ch13-idx-1000005805-2"
></A
><A
CLASS="indexterm"
NAME="ch13-idx-1000005805-3"
></A
><A
CLASS="indexterm"
NAME="ch13-idx-1000005805-4"
></A
>

1;<A
CLASS="indexterm"
NAME="ch13-idx-1000005806-0"
></A
><A
CLASS="indexterm"
NAME="ch13-idx-1000005806-1"
></A
><A
CLASS="indexterm"
NAME="ch13-idx-1000005806-2"
></A
></PRE
></DIV
></DIV
><DIV
CLASS="sect2"
><H3
CLASS="sect2"
><A
CLASS="title"
NAME="ch13-pgfId-2247"
>See Also</A
></H3
><P
CLASS="para"
>The documentation for the standard <CODE
CLASS="literal"
>use</CODE
> <CODE
CLASS="literal"
>overload</CODE
> pragma and the Math::BigInt and Math::Complex modules, also in <A
CLASS="olink"
HREF="../prog/ch07_01.htm"
>Chapter 7</A
> of <A
CLASS="citetitle"
HREF="../prog/index.htm"
TITLE="Programming Perl"
><CITE
CLASS="citetitle"
>Programming Perl</CITE
></A
></P
></DIV
></DIV
><DIV
CLASS="htmlnav"
><P
></P
><HR
ALIGN="LEFT"
WIDTH="684"
TITLE="footer"><TABLE
WIDTH="684"
BORDER="0"
CELLSPACING="0"
CELLPADDING="0"
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="228"
><A
CLASS="sect1"
HREF="ch13_14.htm"
TITLE="13.13. Coping with Circular Data Structures"
><IMG
SRC="../gifs/txtpreva.gif"
ALT="Previous: 13.13. Coping with Circular Data Structures"
BORDER="0"></A
></TD
><TD
ALIGN="CENTER"
VALIGN="TOP"
WIDTH="228"
><A
CLASS="book"
HREF="index.htm"
TITLE="Perl Cookbook"
><IMG
SRC="../gifs/txthome.gif"
ALT="Perl Cookbook"
BORDER="0"></A
></TD
><TD
ALIGN="RIGHT"
VALIGN="TOP"
WIDTH="228"
><A
CLASS="sect1"
HREF="ch13_16.htm"
TITLE="13.15. Creating Magic Variables with tie"
><IMG
SRC="../gifs/txtnexta.gif"
ALT="Next: 13.15. Creating Magic Variables with tie"
BORDER="0"></A
></TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="228"
>13.13. Coping with Circular Data Structures</TD
><TD
ALIGN="CENTER"
VALIGN="TOP"
WIDTH="228"
><A
CLASS="index"
HREF="index/index.htm"
TITLE="Book Index"
><IMG
SRC="../gifs/index.gif"
ALT="Book Index"
BORDER="0"></A
></TD
><TD
ALIGN="RIGHT"
VALIGN="TOP"
WIDTH="228"
>13.15. Creating Magic Variables with tie</TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="684"
TITLE="footer"><FONT
SIZE="-1"
></DIV<!-- LIBRARY NAV BAR --> <img src="../gifs/smnavbar.gif" usemap="#library-map" border="0" alt="Library Navigation Links"><p> <a href="copyrght.htm">Copyright &copy; 2002</a> O'Reilly &amp; Associates. All rights reserved.</font> </p> <map name="library-map"> <area shape="rect" coords="1,0,85,94" href="../index.htm"><area shape="rect" coords="86,1,178,103" href="../lwp/index.htm"><area shape="rect" coords="180,0,265,103" href="../lperl/index.htm"><area shape="rect" coords="267,0,353,105" href="../perlnut/index.htm"><area shape="rect" coords="354,1,446,115" href="../prog/index.htm"><area shape="rect" coords="448,0,526,132" href="../tk/index.htm"><area shape="rect" coords="528,1,615,119" href="../cookbook/index.htm"><area shape="rect" coords="617,0,690,135" href="../pxml/index.htm"></map> </BODY
></HTML
>