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Use of ==> to establish value in a scalar

Posted on 2007-12-01
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Last Modified: 2010-04-21
A book example has the line:

Readonly my $ACTIVE_LOG => '>temp.log<';

I thought => was used for hash list? Why was the => used instead of =  ?
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Question by:lqwest
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3 Comments
 
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by:
Wod earned 75 total points
ID: 20389518
The => digraph is mostly just a synonym for the comma operator:

Comma Operator

Binary ``,'' is the comma operator. In scalar context it evaluates its left argument, throws that value away, then evaluates its right argument and returns that value. This is just like C's comma operator.

In list context, it's just the list argument separator, and inserts both its arguments into the list.

The => digraph is mostly just a synonym for the comma operator. It's useful for documenting arguments that come in pairs. As of release 5.001, it also forces any word to the left of it to be interpreted as a string.
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by:mjcoyne
mjcoyne earned 50 total points
ID: 20389573
Likewise, a hash can be contructed from a comma-separated list:

#!/usr/bin/perl -w
use strict;

my %hash = ('apples', 'red', 'bananna', 'yellow');

foreach my $fruits (sort keys %hash) {
    print "$fruits are $hash{$fruits}\n"
}

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Author Closing Comment

by:lqwest
ID: 31412145
I found some help also in the Perl's Best Practices book - basically has guideline that can be used when trying to decide if a => (aka fat comma) should be use: use it when you can say the symbol becomes blah-blah. Or as in my example ACTIVE_LOG becomes temp.log.
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