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copied!<p><code>*foo</code> is a "typeglob", or "glob" for short. A glob is a structure (as in C <code>struct</code>) with fields named <code>ARRAY</code>, <code>HASH</code>, <code>IO</code>, etc. These fields either contain nothing or a reference. From the perspective of Perl code, they look like very special hashes.</p> <p>The primary purpose of globs is to server as entries for Perl's symbol table. The symbol table holds all symbols that belong to a package and all "truly global" variables (e.g. <code>STDOUT</code>, <code>$1</code>, etc). Without the symbol, there would be no named subroutines, <code>@ISA</code> and <code>@EXPORT</code> wouldn't exist, and neither would <code>@_</code>, <code>$$</code>, etc. [Obviously, globs are most definitely not legacy.]</p> <pre><code>$ perl -E' our @foo = qw( a b c ); our %foo = ( d=>4, e=>5 ); say @{ *foo{ARRAY} }; say %{ *foo{HASH} }; ' abc d4e5 </code></pre> <p>Globs are also used as wrappers around IO objects (file handles). Even <code>open(my $fh, ...)</code> populates <code>$fh</code> with a glob.</p> <p>Globs are very rarely used explicitly in Perl. The one exception is old-style file handles. For example, <code>FILE</code> and <code>STDOUT</code> actually means <code>*FILE</code> and <code>*STDOUT</code> (when used as file handles), which in term are used to get <code>*FILE{IO}</code> and <code>*STDOUT{IO}</code>.</p> <pre><code>$ perl -e'open(FILE, "echo foo|") or die; print readline(FILE);' foo $ perl -e'open(*FILE, "echo foo|") or die; print readline(*FILE);' foo $ perl -e'open(*FILE{IO}, "echo foo|") or die; print readline(*FILE{IO});' foo </code></pre> <p><strong>So why would you want to override <code>*{}</code></strong>?</p> <p>You would want to override <code>*{}</code> if you wanted to create an object that looks like a file handle without actually being a file handle. For example, you could use this override to make IO::Socket object hash-based objects instead of glob-based objects.</p>

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