NAME

Sub::StopCalls - stop sub calls (make it a constant)

SYNOPSIS

    my $i = 0;

    sub boo {
        return foo();
    }
    sub foo {
        $i++;
        return Sub::StopCalls::stop();
    }

    print "$i\n"; # 0
    boo();
    print "$i\n"; # 1
    boo();
    print "$i\n"; # 1

DESCRIPTION

Basicly you can do the following in a function to mean "Hey, You! You, who called me, stop calling me, I will always return the same result":

    return Sub::StopCalls::stop( @result );

Still no idea how to use? Ok, here some use cases:

USE CASES

conditional constants

Classic if DEBUG thing:

    sub debug {
        return Sub::StopCalls::stop() unless $ENV{'MY_APP_DEBUG'};
        ...
    }

Or logger:

    package My::Logger;
    sub warn {
        return Sub::StopCalls::stop() if $self->{max_level} < LEVEL_WARN;
        ...
    }

accessors to singletons

    package MyApp;
    
    my $system;
    sub system {
        $system ||= do {
            ... init system object ...
        };
        return Sub::StopCalls::stop( $system );
    }

hooks, triggers and callbacks

    sub trigger {
        my $self = shift;
        my @triggers = $self->find_triggers(caller);
        return Sub::StopCalls::stop() unless @triggers;

        ...
    }

FUNCTIONS

stop

Does the job. Replaces call on upper level with whatever is passed into the function. Expected usage:

    return Sub::StopCalls::stop(...) if ...;

Some details

context

Result depends on context of the call that is replaced. Nothing special about void or array context, however, in scalar context if more than one argument passed into the function then number of elements returned:

    # replaces with undef
    sub foo { return Sub::StopCalls::stop(); }
    # replaces with 'const'
    sub foo { return Sub::StopCalls::stop( 'const' ); }
    
    # replaces with number of element in @a,
    # but only if @a > 1, otherwise first element or undef
    return Sub::StopCalls::stop( @a );

arguments

Arguments of the replaced call also "stopped", for example:

    for (1..10) {
        function_that_stops_calls( other(...) );
    }

other(...) called only once. Second iteration just jumps over.

It's good in theory, but in some situations it can result in bugs.

threads

This module is not thread-safe at the moment.

AUTHOR

Ruslan Zakirov <ruz@bestpractical.com>

LICENSE

Under the same terms as perl itself.

cpanm Sub::StopCalls

perl -MCPAN -e shell
install Sub::StopCalls