... how would we know that this code is doing caching activity?

I've seen some cases where people take the trouble to provide a report on caching effectiveness -- basically, you want to know how many times "first_line" was called, and of those times, how often you hit on a cached value.

That sort of thing is easy to add -- here's how it might look, adding to dragonchild's proposal, which is very clear and clean: 

my %cache;
my ($ncalls, $nhits);
sub first_line
{
    my ($filename) = @_;
    $ncalls++;
    if (exists $cache{$filename}) {
        $nhits++;
    }
    else {
        open( my $fh, $filename ) or die "Cannot open '$filename': $!\
+n";
        $cache{$filename} = <$fh>;
    }

    return $cache{$filename};
}

END { print "first_line returned cached value $nhits times in $ncalls 
+calls\n" }

[download]
Usually you'd want the report to be conditional on a run-time option -- e.g. the user includes a "-v" or "-d" flag when running the script from a command line to select "verbose" or "debug" mode.

In reply to Re: Cache Subroutine Return Value by graff
in thread Cache Subroutine Return Value by souravdas

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.