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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.