You don't need to overload an inbuilt function IF you define one of the same name and call it with the ampersand prepended, i.e. &time will execute a user-defined subroutine named time if it exists. Otherwise, you can check out dchetlin's tutorial Overloading '=' for some info on how to overload inbuilt functions.

As to the first problem: you can wrap require Time::Hires in an eval inside a BEGIN block, and if that eval fails, print a warning (if appropriate) and set a flag that tells your program to use the internally defined routine. If the eval succeeds, call import Time::Hires and you'll have the symbols imported.

#!/usr/bin/perl -w

use strict;

use vars '$internal';

BEGIN: {
     eval "require Time::Hires";
     if ($@) { # if it failed
          print "Can't load Time::Hires, falling back to own routines\
+n";
          $internal =1;
     } else {
          import Time::Hires;
          $internal = 0;
     }
}
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Philosophy can be made out of anything. Or less -- Jerry A. Fodor

if ( eval { require Time::Hires } ) {
    # The require was successful
} else {
    # It was unsuccessful
}
[download]

Cheers,
Ovid

Update: Whups! Since I hadn't used Time::Hires before, I wasn't aware of what it does internally. I suspect that autark's correction below is appropriate.

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But the function time() from Time::HiRes will not be imported. To make this binding between &main::time and &Time::HiRes::time we have to this at compile time:

BEGIN {
    eval { require Time::HiRes; import Time::HiRes qw(time) };

    if($@) { warn "Unable to import Time::HiRes\n" };
}
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Without the BEGIN, the binding of time to the correct function would not happen:

eval { require Time::HiRes; import Time::HiRes qw(time) };
print time()
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Would produce f.exs: 976556706. While

BEGIN { eval { require Time::HiRes; import Time::HiRes qw(time) }; }
print time()
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Would produce the correct time using the Time::HiRes::time function: 976556789.394509.

Autark.

#!/usr/bin/perl -w
use AUTOLOADER;
sub AUTOLOAD {
 $v = $AUTOLOAD;
 $v =~ s/.*:://g;
 if($v eq "SomeFunctionFromHires")
 {
        #if this is called, it didn't work
        require qw(c:\temp\hires.pm);
 }
}

&SomeFunctionFromHires();
&foo;
&SomeOtherFunctionFromHires();
&secondfoo;
1;

Here's what is in the phony Hires.pm:

sub foo
{
print "foo!";
}

sub secondfoo
{
print "secondfoo!";
}

1;

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