Why do you need to escape a string used as a paramater?

awohld has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Why do you need to escape a string used as a paramater? by Zaxo (Archbishop) on May 24, 2005 at 05:16 UTC
That's not an escape as in quotes, it takes a reference to $intr_html. That speeds up parameter passing by removing the need to make a copy. After Compline, Zaxo	[reply]
Re^2: Why do you need to escape a string used as a paramater? by bart (Canon) on May 24, 2005 at 08:20 UTC
That speeds up parameter passing by removing the need to make a copy. That's only part of the story. It's also, even most of all, the way HTML::TokeParser distinguishes between literal HTML in a string, and a string holding the file name of a file containing the HTML: `$p = HTML::TokeParser->new( $filename ); $p = HTML::TokeParser->new( $filehandle ); $p = HTML::TokeParser->new( \$document );` [download] Note cases 1 and 2. Choosing this convention instead of the other way around, was indeed the wisest choice with regard to efficiency.	[reply] [d/l]
Re: Why do you need to escape a string used as a paramater? by Dietz (Curate) on May 24, 2005 at 05:26 UTC
You are passing a reference to tell the constructor to read from its referent. If you omit the backslash the constructor thinks you want to pass a filehandle or a filename and this will not work for you most likeley because you don't have a filehandle or filename named $intr_html. 'perldoc HTML::TokeParser' tells you more ;-)	[reply]
Re: Why do you need to escape a string used as a paramater? by monkfan (Curate) on May 24, 2005 at 05:19 UTC
Why is the "\" needed??? Because the method is constructed in such a way that it requires a 'scalar reference' to be passed into it. Seems to me it's a standard practice in creating a new object. Regards, Edward	[reply]
Re: Why do you need to escape a string used as a paramater? by kprasanna_79 (Hermit) on May 24, 2005 at 05:33 UTC
Hai awohld, The HTML::TokeParser takes argument as scalar reference. To know more about reference please read this, which gives u more idea about the reference. --prasanna.k	[reply]
Re: Why do you need to escape a string used as a paramater? by Aragorn (Curate) on May 24, 2005 at 08:01 UTC
The "\" in this case makes a reference to the variable `$intr_html`. When a "normal" variable is given to `HTML::TokeParser::new`, it is taken to be a filename to open and read. When a reference is given, it is taken to be a "pointer" to the text in `$intr_html` to be parsed. See perlreftut for a tutorial on references and perlref for all the details. Arjen	[reply] [d/l] [select]
Re^2: Why do you need to escape a string used as a paramater? by Tomtom (Scribe) on May 24, 2005 at 09:09 UTC
Could we consider a reference "\" in Perl the same thing as a "&" in C, for example ? Tomtom	[reply]
Re^3: Why do you need to escape a string used as a paramater? by Aragorn (Curate) on May 24, 2005 at 09:38 UTC
Superficially, yes. "Under water", there's a lot more going on with Perl references, like automatic memory management. Arjen	[reply]