in reply to Importing Time::HiRes::time at run-time (and failing)

because time is not a function but a built-in operator.

When perl compiles your function, it checks if time has been redefined in the current package and if so, it emits opcodes to call a subroutine called "time", otherwise, it emits the time opcode (pp_time). As you are defining time after compilation, the time call is being compiled as the built-in and so the function from Time::HiRes never gets called.

You can work around it as follows: 

sub new {
    require Time::HiRes;
    return bless { t => Time::HiRes::time() }, 'P'
}

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Re^2: Importing Time::HiRes::time at run-time (and failing)
by grinder (Bishop) on Apr 20, 2006 at 15:10 UTC

    Aha! Thanks for the cogent explanation. Along with some advice from bart on the chatterbox, I came up with the following proof-of-concept solution.

    #! /usr/local/bin/perl -l

package P;

sub new {
    my $class = shift;
    my $mod   = shift;
    eval "use $mod ()";
    my $self = {};
    if ($@) {
        $self->{_time_func} = sub { time };
    }
    else {
        $self->{_time_func} = sub { Time::HiRes::time() };
    }
    return bless $self, 'P'
}

package main;

my $p = P->new( shift || 'Time::HiRes' );

print $p->{_time_func}->();
sleep 2;
print $p->{_time_func}->();

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    You can run this, and if T::HR is installed, you get fractional times. Pass it junk on the command line, and then T::HR is not loaded (which simulates what happens on an installation that lacks it, or fails to load) and integer seconds come out.

    In the real world, the _time_func business will be hidden from the user, they just get back fractional seconds, or not.

    • another intruder with the mooring in the heart of the Perl

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[d/l]
      you can simplify it a bit replacing the eval "..." by a eval {...} and returning a reference to Time::HiRes::time instead of it wrapped inside an additional sub: 
      package P;

sub new {
    my $class = shift;
    my $self = {};

    $self->{_time_func} =
      eval { require Time::HiRes }
        ? \&Time::HiRes::time
        : sub { time() };

    bless $self, $class
}

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