CONTENTS

NAME

Mojo::Promise - Promises/A+

SYNOPSIS

use Mojo::Promise;
use Mojo::UserAgent;

# Wrap continuation-passing style APIs with promises
my $ua = Mojo::UserAgent->new;
sub get {
  my $promise = Mojo::Promise->new;
  $ua->get(@_ => sub {
    my ($ua, $tx) = @_;
    my $err = $tx->error;
    $promise->resolve($tx) if !$err || $err->{code};
    $promise->reject($err->{message});
  });
  return $promise;
}

# Synchronize non-blocking operations (all)
my $mojo = get('http://mojolicious.org');
my $cpan = get('http://metacpan.org');
Mojo::Promise->all($mojo, $cpan)->then(sub {
  my ($mojo, $cpan) = @_;
  say $mojo->[0]->res->code;
  say $cpan->[0]->res->code;
})->catch(sub {
  my $err = shift;
  warn "Something went wrong: $err";
})->wait;

# Synchronize non-blocking operations (race)
my $mojo = get('http://mojolicious.org');
my $cpan = get('http://metacpan.org');
Mojo::Promise->race($mojo, $cpan)->then(sub {
  my $tx = shift;
  say $tx->req->url, ' won!';
})->catch(sub {
  my $err = shift;
  warn "Something went wrong: $err";
})->wait;

DESCRIPTION

Mojo::Promise is a Perl-ish implementation of Promises/A+.

ATTRIBUTES

Mojo::Promise implements the following attributes.

ioloop

my $loop = $promise->ioloop;
$promise = $promise->ioloop(Mojo::IOLoop->new);

Event loop object to control, defaults to the global Mojo::IOLoop singleton.

METHODS

Mojo::Promise inherits all methods from Mojo::Base and implements the following new ones.

all

my $new = Mojo::Promise->all(@promises);
my $new = $promise->all(@promises);

Returns a new Mojo::Promise object that either fulfills when all of the passed Mojo::Promise objects (including the invocant) have fulfilled or rejects as soon as one of them rejects. If the returned promise fulfills, it is fulfilled with the values from the fulfilled promises in the same order as the passed promises. This method can be useful for aggregating results of multiple promises.

catch

my $new = $promise->catch(sub {...});

Appends a rejection handler callback to the promise, and returns a new Mojo::Promise object resolving to the return value of the callback if it is called, or to its original fulfillment value if the promise is instead fulfilled.

# Longer version
my $new = $promise->then(undef, sub {...});

# Pass along the rejection reason
$promise->catch(sub {
  my @reason = @_;
  warn "Something went wrong: $reason[0]";
  return @reason;
});

# Change the rejection reason
$promise->catch(sub {
  my @reason = @_;
  return "This is bad: $reason[0]";
});

finally

my $new = $promise->finally(sub {...});

Appends a fulfillment and rejection handler to the promise, and returns a new Mojo::Promise object resolving to the original fulfillment value or rejection reason.

# Do something on fulfillment and rejection
$promise->finally(sub {
  my @value_or_reason = @_;
  say "We are done!";
});

race

my $new = Mojo::Promise->race(@promises);
my $new = $promise->race(@promises);

Returns a new Mojo::Promise object that fulfills or rejects as soon as one of the passed Mojo::Promise objects (including the invocant) fulfills or rejects, with the value or reason from that promise.

reject

$promise = $promise->reject(@reason);

Reject the promise with one or more rejection reasons.

resolve

$promise = $promise->resolve(@value);

Resolve the promise with one or more fulfillment values.

then

my $new = $promise->then(sub {...});
my $new = $promise->then(sub {...}, sub {...});
my $new = $promise->then(undef, sub {...});

Appends fulfillment and rejection handlers to the promise, and returns a new Mojo::Promise object resolving to the return value of the called handler.

# Pass along the fulfillment value or rejection reason
$promise->then(sub {
  my @value = @_;
  say "The result is $value[0]";
  return @value;
},
sub {
  my @reason = @_;
  warn "Something went wrong: $reason[0]";
  return @reason;
});

# Change the fulfillment value or rejection reason
$promise->then(sub {
  my @value = @_;
  return "This is good: $value[0]";
},
sub {
  my @reason = @_;
  return "This is bad: $reason[0]";
});

wait

$promise->wait;

Start "ioloop" and stop it again once the promise has been fulfilled or rejected, does nothing when "ioloop" is already running.

SEE ALSO

Mojolicious, Mojolicious::Guides, http://mojolicious.org.